Illinois State's resume is not string. They only played 4 opponents of note:
http://goredbirds.com/schedule.aspx?path=mbball
11/14 at TCU (NIT 4 seed).. lost 71-80
01/14 Wichita State .......... won 76-62
02/04 at Wichita State ....... lost 86-45
03/05 vs Wichita State ....... lost 71-51
They caught Wichita on a bad night at home. But the return game was UGLY. And they were not able to do anything about it in the MVC Championship Game.
Like Syracuse (terrible on the road), Cal and Iowa, a #1 seed in the NIT is probably right.
Frankly their win is less impressive than BYU's over Gonzaga on 2/25 in Spokane
79-71. But they failed to press their case by getting blown out by Saint Mary's 81-50 on 3/6 in the WCC semi-final. And the WCC was considerably stronger than the MVC this year, especially the middle and bottom teams.
Monmouth's case is even worse. They did have a quality loss, 71-70 OT, to South Carolina, but got then beat by Syracuse 71-50 back in mid-November, in what were basically warm up games for all involved. After that they have not played anyone of any note. And empty resume basically.
I am not taking anything away from terrific runs in conference, but it's not like that was against ACC or even Pac12 competition.