Which rules have they actually broken?
They announced they were joining a new breakaway competition, all planned without the approval of the PL. publicly put out a press release which brings the game into disrepute. Undermines other clubs.
https://thesuperleague.com/press.html
I mean, what have you been seeing the past few days? They only withdrew due to the overwhelming public backlash. There needs to be a deterrant of some sort.