Just to put things in perspective, Gonzaga at St Marys, which tipped off at 10 pm EST, drew little over a million on ESPN. It was a rivalry game with big implications for both teams, but at the same time for your average American, regular season college basketball isn't must see TV.
But I think the bigger point is the power of ESPN over FS1. 10 years since its launch, FS1 is still struggling to compete outside of college football season, even then Im sure ESPN still wins. Nobody thinks to put FS1 on, while ESPN on in the background at home or at the bar is a given. In my area, ESPN is on channel 12 while FS1 is 63 or 64.