They made disco. I fucking hate disco, but without them and their music behind Saturday Night Fever, disco wouldn't have had the crazy mass appeal that it had. Predictably, almost everything else in that genre was a pale imitation of what they did
The really strange thing about the Bee Gees is how they are forever labeled as disco.
In the 60s their comparison was The Beatles. They released 22 studio albums (not counting soundtracks like Saturday Night Fever) over 36 years. They covered rock, folk rock, R&B, soul, funk, country, dance music, etc. Really, only tiny fraction of songs over that period were actual disco songs. Before Saturday Night Fever, their 60s/early 70s music was played on classic rock stations. Even their mid 70s music wasn't called disco before that movie, which was only part of the reason that in 1978 the Bee Gees had the biggest one year peak of any artist ever in terms of chart success (counting songs they wrote and produced for others, including their brother). They wrote the #1, 2, 4, 6, 8, 11, 14, 19, and 45 songs that year. Only 4 of those songs were. from Saturday night fever. Nobody else ever did anything like that. Not peak Elvis, not peak Beatles, not peak Prince, not peak Michael Jackson.
In the 80s and 90s they wrote songs that were massive, best of career hits for other artists, but couldn't get their own music played anymore and became the butt of jokes, some of which also should have also been massive hits. They had one song, You Win Again, that hit #1 all over the world except in the US where radio stations refused to play it, because, hey, the Bee Gees are disco and we don't play disco.
Music is the only art form where people get punished and not rewarded for versatility. Imagine if movie theaters refused to show any comedy or action movies from Spielberg after Schindler's List because, hey, Spielberg is a drama director. And while we're at it, let's pretend he never made movies like Jaws, ET, Raiders, etc. That's effectively what happened to the Bee Gees after Saturday Night Fever.