After watching the videos featuring the hair models, then watching the videos featuring Tyra, then watching the "behind the scenes" video of Ty baby and Andre:
http://www.youtube.com/watch?v=o7pT3NbITio
I am convinced it is not 100% the models fault. It is the fault of the director for the format in which they are expected to shoot these videos. They want them to do it in almost one take, of course under 3 minutes, and the studio in which they are doing this video is very limiting. You can't do the styles that they are trying to do in under 3 minutes. To do a full head of twists you need at least 1-6 hours, but the director aren't going to give them the time needed to complete the style. So I blame the director more than anyone else.
For all we know, the models had no idea that this was the way that these videos were going to be shot until the day they rolled up on the set and they said *** it, I want that check so they went ahead and rolled with it. Who knows but all I know is that the women are more than likely doing the "best" they can given their situation...