That team had gone 6-12 the year before and had just lost its most talented player to the NBA lottery (Leornard). It was not only Bruce Weber, even after his removal, Illinois was not projected to make the NCAA tournament. Groce did overachieve in his first season, that much is true, it is revisionist history to think otherwise.
The program (personnel-wise) was not in good shape either as mentioned in previous posts. Every new coach would have to replace ONE (senior) class (2009 class for UI), but Groce also had to replace the 2010 class (all washed out before Groce), the 2012 class (empty), and half of the 2011 class that had players that clearly did not belong at that level (Ibby, Langford, Shaw). That is 3.5 classes, not an easy task.
It was a dire situation, yet that does not excuse Groce for having failed in his overall tenure at UI. In year 5, the program should have been much further ahead.