If they tried to impose the rules that Apple does, both third party developers would leave their store.

Which to be fair has also been a problem for Apple in the Mac App Store.

Probably a mix of not having much to loose, trying to gather some good publicity and fear that the regulators would see them as some kind of "repeat offender" and punish them harder than Apple, Google et. al. if they dragged their feet.

Precisely, they wish they had the leverage to enforce revenue splits from alternative payment systems.