Well, if one goes back a ways, there are more Big Ten schools who have had them. As another poster mentioned, U of M did have Kris Humphries. Even Iowa had one (Ricky Davis) but that's going back to the nineties.
Your general point is correct, though, the Big Ten as a whole hasn't been a primary destination of one-and-dones in recent years. Since 2006, here are the number of one and dones (who were drafted) by Big Ten school:
Ohio State: 6 (3 were from the 2007 team that went to the national championship)
Indiana: 2
Michigan State: 1
Maryland: 1
Total 10
In contrast, over that same time period:
ACC (22)
SEC (27 - mostly from KY of course)
Big 12 (17)
Pac 12 (20)
As one might guess from following college basketball, one and done recruitment has been fairly consolidated into a relatively small number of programs. Over the time period mentioned above, 9 schools have accounted for 65% of the drafted one and done players and only 19 schools have had more than one player.
Source:
https://herosports.com/news/one-and-done-rule-list-college-basketball-nba-visualized