But even if they had bubbled, Neither Michigan nor Notre Dame were infected in Fargo and Albany. The results to the tournament would have been the same. ND would not have been allowed in and Michigan would have been kicked out this afternoon.
I don't know how the bubble would have worked, though. The sports that bubbled last year (NHL, NBA) required a certain amount of isolation time before the games and practices started. This would not have been possible with the conference championships just ending 5 days ago.
I know the basketball tournament did a bubble in Indy with a similar timing situation. The way the winter sports season has gone, I think they got really really lucky that only 1 team had an issue coming in. Now that the remaining 16 teams have been in Indy for a week and a half, the bubble concept should be helping prevent any further disturbances.
If hockey followed that plan, the bubble would only really protect the frozen four teams, not really the other 12.