The lack of a NCAA tournament, in person workouts, and combine just allowed Okoro's flaws to go unnoticed. I'm sure he would drop on teams boards if those thing had occured.
Okoro just looked bigger and more versatile in college because of the lesser competition. Okoro also was more maturely built than a typical freshman basketball player.
Team would have question how versatile he actually was once they got measurements and worked out against NBA talent level. Players also tend to shine in the tournament and there is a reshuffling of the board because of it.
If teams were able to have in person workouts, I imagine that the Cavs would have lined up players to workout against him to see his defensive versatility. My guess is the Cavs would have expected an almost TT level predraft workout and they would have walked away knowing he couldn't guard PFs for sure. They probably would have also questioned how well he could guard speedy guards and big wings.