It wasn't quickly. Parler has been around for two years, and the kind of material that got them finally kicked out of places has been there from near the beginning. Parler's lack of moderation of user content has been in violation of Apple and Google's rules for all that time.

I bet if someone had started a service similar to Parler but non-political, where people posted massive amounts of death threats and hate speech but directed at people for non-political reasons and that service utterly failed to moderate, Apple and Google and the rest would not have given them two years. They would have been gone in a week.