In Big 12 there are 9 teams that can beat anybody on a given day, where as Big 10 and ACC have several teams at the bottom that just can't compete. SEC is Alabama (and maybe LSU) and everyone else.
https://www.si.com/college-football/video/2017/08/18/big-12-nations-deepest-conference
https://www.si.com/college-football/video/2017/08/18/big-12-nations-deepest-conference