Except that this regulation only applies to so-called gatekeepers, so it doesn't affect 99.9% of the companies out there. Even if you made your own phone with it's own app store, until you have a sizable part of the market, you won't be a gatekeeper under the DMA.

A lot of sensible regulation provides escape hatches for smaller companies to avoid the huge costs of compliance. The exception is where there should be absolutely no exceptions, like medical regulation or privacy.

In this case regulation is the only thing causing competition, Apple was doing perfectly fine discouraging competitors themselves.