Because more often than not, you are gonna get plenty challenge in conference play. Even in a "down" B10, its still a tough ass conference. So why play a Kansas, Duke, Nova, etc, etc.....? If your aspirations are getting to a SW 16, and beyond, wins= high seed= easier path to a SW 16. Now I'm saying you go out a play a bunch of 200+ teams. BUT.....play some upper echelon mid-major teams---teams expected to win/compete for their conference titles; like MVC, OVC, A-10, sort of teams. Mix in a game, maybe two vs a Kansas, Nova, type of team(s). Then get those automatic wins, i.e. North Texas, E.Illinois, etc, etc...Not to mention there's the ACC/Big 10 game. Get to 13/14 wins in the Big 10, and you're probably looking at a 3/4 seed....
In a year like this year, you'd be nuts to play some craxy, tough OOC schedule. Purdue, Michigan, Illinois, Ohio State and Marylnad are all preseason Top 25; With MSU and Indiana just outside the Top 25---MSU 26th/IU 27th. With Purdue/Michigan in the Top 10, and Illinois just outside the Top10, at #11.
SOS is a factor----But THE factor is wins. You rack up some losses to Kansas, Texas, Kentucky, etc, etc....then lose 5-6-7 games in a tough B10, and your not getting a high seed with 8, 9 or 10 losses.
Its all about the seed. Its why you rarely see Top tier teams go on the road, vs quality, OCC teams.