There have been tensions between the FIDE organization and top players like Carlsen since the latter have been promoting an alternative chess organization around Freestyle chess (aka Chesss960), which has slightly different rules.
I.e. this is less about "dress code enforcement" and it is more about "Carlsen is fed up with the FIDE organization in general".
They're competing for the time and attention of the players. If there are two competitions on the same day, players will have to choose which competition to play in. That in itself will determine where the sponsorship money goes unless they can agree not to put events on at the same time. They won't do that because it isn't in either group's interest.