It is because of the other 2 choices, the one game is too late, and the remaining game, Nebraska, well, they know that they can sell out that game without it being Homecoming. Having Ohio as the Homecoming opponent, in a sense, forces people to sort of care more about the game, because of all of the Homecoming stuff going on and surrounding the game and leading up to the game. They are hoping to get alot of students to go to the game.
So basically this just leaves us with one total "no one cares" kind of game in the game vs Kent St. TCU will sell out, Col St is a road game, Ohio is homecoming and so should be a better than otherwise turnout, and the rest are conference matchups.
Simple economics. Now there is a playoff, soon it will be an 8 game playoff. We have a Conf Title game, we have Maryland, Rutgers, Nebraska and Penn St in the conference now and may go 3 years in a row sometimes without seeing certain teams in the East Division. We are back to playing outdoor football in a stadium designed to encourage tickets to conf games being hard to come by because of the limited # of seats available. If the Gophers really start kicking arse, they are hoping demand will be so high to see games that people who can't get tickets to see Nebraska or Michigan or Ohio St or Wisconsin or Iowa or PSU or MSU, will start going to games vs NW, Illinois, Indiana, Rutgers, Maryland and Purdue and might even start going to ooc games vs the likes of Ohio and Kent St as well, aided by having homecoming opponents being ooc opponents, for one.
But most of that is just my theory/opinion.