T'was character assassination.
And piss poor sloppy writing. They could have at least come up with a plausible reason for an army to freeze in the cold, shit.
It is as simple as:
Davos: "We've been here too long Your Grace. We've eaten through most of our supplies and there isn't so much as a kernel of corn within 50 miles of here. What the early snows didn't destroy in the unharvested fields, brigands and stragglers have taken. We must march back to the Wall, or treat with Manderley or take White Harbor from him now or we will starve to death! We can always have the fleet bring up supplies to the coast!"
Stannis: "Never. Our aim is Winterfell and Bolton. The cold effects us all the same. We march tomorrow. Ready the siege engines for transport."
Davos: "Your Grace, the cold, it has made the tension lines snap, and the metal brittle. The engines are useless. Without them we cannot take a castle as well built as Winterfell. Aye, its cold all the same, but they have walls and food in their bellies. We must withdraw! Live to fight another day."
Stannis: "No. We will march and win. Or march and die. There is no turning back."
The show really takes a downturn when they started writing their own original story lines. They're fairly bad writers.
They don't care about logical consistency at all. For instance, multiple times in season 5, once by Littlefinger, and once by Benioff himself, Stannis is referred to as having one of the finest military minds in Westeros.
And yet he does nothing to show that at all, and in fact, by letting RAmsay Bolton destroy all of his shit with 20 men and then letting Ramsay just surround him on the field of battle, looks like one of the dumbest military minds in Westeros.
When they chose to only do 7 1/2 seasons it obviously meant story lines had to be cut and various side character plots had to be given to main characters. But the problem is, they SUCKED at doing it in a logical manner.
Here are all of the absolutely dumb fucking story lines in 5:
1. Sansa being sold to the Boltons. Now, perhaps it makes some logical sense for Littlefinger to make his move on the Throne, what with Twyin dead, Tommen being a weak ruler, Cersei doing everything she possibly can to fuck over the Tyrells, and the Freys essentially taking command of the Riverlands. Ally the Vale with the Boltons and Freys, and you might be able to march South.
But Littlefinger specifically says to Sansa that he would put his money on..STANNIS WINNING. Let me say that again, Littlefinger tells Sansa that he thinks STANNIS WILL BEAT THE BOLTONS. So then, why would you ally with the Boltons if you think they're about to lose the fucking war? Now, I get it that Littlefinger probably figures he has no shot at allying himself with Stannis, what with what happened at the Blackwater. But there are other options out there...like, ya know, the Tyrells, whom Littlefinger already has a relationship with. Or the Martells, who despise the Lannisters entirely.
2. Dorne is just a total mess. I wasn't a huge fan of Dorne in the books, and I understand not wanting to introduce 8 Sand Sankes, Arianne, Quentyn, and a Prince Doran who is a much larger player in the books. That's a lot of new characters for a TV show 5 seasons in. Ok. So we have to condense the story and they chose to use the woman who we've already met in season 4. Fine. But, holy fuck is it stupid. First of all, every scene that involves the Sand Snakes is just cringe.
But the real issue, and its the issue that plagues the entire season, and eventually the rest of the series going forward, is the total lack of political consequences in any meaningful way. George doesn't let that happen, and when they're following George, you got to see that. JOffrey sucks as a ruler and is believed to be the child of incest? Alright, well here comes a crowd riot wherein Sansa almost gets raped. Ned telling Cersei he knows she fucks Jaime, ordering Twyin to the Capital and the arrest of the Mountain, and then not seizing the Throne to prevent Cersei and Joffrey from taking him out? Ok, there goes his head. Same with Robb.
But here, Elia and the Sand Snakes kill the Prince of Dorne and his son and...nothing. THey just...take over. With four people. The entire Dornish army just follows them w/o question. No political consequences at all in Dorne. We're just supposed to assume that assassinations and coups are just easy peasy, over and done.
Which flies totally in the face of what we know about assassinating beloved leaders. Littlefinger killed Lysa because she couldn't keep her mouth shut about John ARryn. Had people found out, they'd have executed Littlefinger in the Vale. But Elia? Nah, who cares bro...
Then, when they try to still have some semblance of a political drama as opposed to a series based around 3-4 Major Action Sequences a season with various annoying plot points in between, you get the stupidity of Jon being killed. So, they kill him for allowing Wildlings in...after letting the Wildlings in??????? Like....they're already in. Thorne LET THEM IN. In the books, they kill him because he's about to take a Wildling Army South and fight for Winterfell, clearly violating his oaths. By killing him, they actually stop that action. Here..they stop nothing. They do nothing. All of the Wildlings are already fucking south of the wall. Too late.
This continues into the later seasons. Cersei, after being found out as a incestuous, not only resumes her role as Queen w/o so much as a peep from the commoners or Lords, but she then kills off 1) Mace, Margaery and Loras Tyrell. One is the head of a beloved House who feeds the capital. His daughter is a beloved Queen who goes out of her way to help the poor and the other is a popular swordsmen who was won multiple tourneys. 2) The High Sparrow, a religious revolutionary who has captured the hearts of the city and the faith 3) Kevan Lannister, the eldest stateman of House Lannister and countless others.
And what happens to her? Well, Varys talks a little about how she's hated by the common folk but...that's it. I mean sure, Dorne and Highgarden join her enemy, but they die in the span of two episodes. Totally and completely. And when Cersei loses, it has zip to do with her poor ass decision making. Randomly killing off your allies, your very rich allies (when you're House is actually now broke), is a terrible idea. But she pays no price. She lost for the same reason whoever loses to Daenerys in the books will lose. Whether that's Cersei or fAegon or even Stannis on the Throne when she gets to Westeros. George has beaten us over the head time and time and time again: they'll lose because Daenerys has dragons and they don't. Cersei never paid once for her shitty decisions.
Which makes their decision to focus the end of the series on the political element truly disastrous. They stopped giving a fuck about showing any real political ramifications in season 5.
Also, I used to be a fan of keeping Beric and not bringing in Lady Stoneheart. I didn't like the character. But, seeing how they had no idea whatsoever how to use Jaime if he wasn't tied to Cersei (and probably just making the decision to keep Jaime with Cersei because they liked Lena too much), I'd have rather had Lady Stoneheart and the plot from the books. Because when they have to get Jaime out of KL for Cersei to 1) Beclown herself and get arrested by the Faith and 2) Blow up the Sept, causing the death of their son, they do so in the clumsiest, most boring ways possible. First, was this Dornish mission, that sucks ass. Later, it's the pointless Siege of RIverrun.
Then you've got the really idiotic shit Jaime puts up with. Like, ok dude, you love her even though she cheated on you with Lancel. But, um, she just caused YOUR SON to jump out of the window......and you're still fucking her? What a waste of a character arc.
/rant