He disclosed his relationship with Oracle four months before the judge asked both companies to "name their shills" [1,2]. It was a highly unusual and controversial order [3], so it's not like Mueller, or indeed anybody, could have predicted this and "come clean" in advance.
Also note that Oracle had that one name on its list. Google had a much longer list. Further, I think the judge erred by not requiring both sides to disclose relevant PR ties, because really, it's the PR companies that oversee the shilling [4, 5]