Nobody not even Mike and her teams has a concrete reason why they got denied, the blonde guy says he "was giving literary no reason" and simply was told Mike was No good, there is 2 Holostars in the tournament but I feel Cover would be really stupid to ask to remove someone over her being in the same tournament as 2 stars who never even interacted with Rushia, some other people are saying MafuMafu is actually good friend with the TO of the tournament and also apparently there's precedent of some other vtuber saying she got denied participating due to "being involved in several controversies", but all anyone has is speculation.
Gotta say even though I have said before that I dislike Mike now a days, this feels like a really shitty move from the tournament, the guy from her team said he summited his team a while ago and got the all ok back then, and then after the announcement he gets told plainly its not ok anymore, literary a day before the tournament, which is the reason the other 2 guys couldn't participle even with another teammate since the tournament is literary today so where are they even gonna find one, IMO is fine is the tournament didn't want Mike in it, and she kinda deserves it, but walking back on their word a day before the event is kind of a bitch move.