Imo biggest issue is that professors are incentivized to research, not teach. 101 classes have a high percentage of non-major, disinterested students, so the good teachers don't want to teach them. So the combination of undergrads being an annoyance that must be dealt with in order to do the real job of research, and the teachers who actually take that annoyance seriously not teaching this class means 101 classes are commonly not updated and little work is put into them by the teachers. AP courses are designed by people whose job is designing courses, not people whose job is research and "oh yea teach these undergrads too."