I am not sure who you are counting. There were really only 3 bigs on the active roster, since Finke redshirted just before their season started.
And only 2 of them were over 6'7". Here is their roster-
http://www.fightingillini.com/sports/m-baskbl/m-baskbl-roster.html
The Illinois' bigs were-
Leron Black- listed at 6'7", 220 but probably only 6'6" and not quite 220- played pretty well for a freshman, but way undersized for a Big Ten power forward
Maverick Morgan- 6'10"- I have seen enough to conclude he is not a Big Ten level player. Despite the lack of big men, he played under 9 minutes per game (mostly garbage time).
Nnanna Egwu- 6'11, 250 (probably nowhere near 250), but he was the only marginal quality big man on the team the last 2 years., but underwhelming production.
Michael Finke- 6'10" freshman with good skills, but who was a lot skinnier and weaker that Groce expected despite an intense workout program last summer. Despite the void of quality bigs on Illinois,
Coach Groce insisted he redshirt. There were reports that the Finkes weren't happy about it.
So for a team trying to compete in a league loaded with good big men, Illinois' entire stable of big men consisted of Nnanna Egwu and 2 freshmen (one undersized and the other lacking talent). And now Egwu is gone (graduated). IMO, Finke will not even be able to replace the meager numbers the Illini lose next year from Egwu.
So despite having good quality and depth at guard, Illinois could do no better than 9-9 in the Big Ten. Their post-season was extremely disappointing. They were 1 and done in the Big Ten Tournament (blown out by a mediocre Michigan team that didn't even make the NCAA or the NIT Tournaments), then Illinois missed the NCAA, then went 1 and done in the NIT with an even more lopsided blowout loss to an Alabama team that finished with a losing record in the SEC (8-10), and a disappointing 19-15 overall, and fired their coach.
Here are the stats for the only 3 big men who played. These are amazingly poor numbers for an entire frontcourt of a Big Ten team--
Egwu- 6.5 ppg and 5.9 rpg
Black- 5.1 ppg, 4.3 rpg
Morgan- 2.5 ppg, 1.5 rpg (these numbers make Mike Shaw look like a superstar)
Totals- 14.1 ppg, 11.7 rpg for their entire frontcourt
And as mentioned, now Egwu is gone. Finke, Black, and Morgan are the only bigs returning. So you'd think Groce would go out and sign some quality big men? But the only recruit even close to a "big man" was D.J. Williams, who is an undersized small forward who plays more on the wing. They did just get a 5th-year transfer 6'10" Mike Thorne from Charlotte. He'll help a little as a 1-year stopgap, but I have seen him play, and he is also not a Big Ten caliber player. IMO, Illinois is going to struggle again in the Big Ten next year and in future years until Groce can recruit some quality bigs.