Why would Apple, Google, or any of the EU Phone OS developers bother creating a new feature that they will immediately be forced to allow everyone to use?
Because new hardware/interoperability features are an opportunity to sell more hardware. Apple still gets to make and sell accessories, their product just has to compete on the merits with other products in the segment. People will keep buying Airpods even if Sony's can hand-off between Apple hardware because Airpods are a great product that can stand on their own.
Alternatively, look at Google trying to take control of the web/HTML with their Web Environment Integrity API proposal. If the web was a "Google Protocol" rather than a W3C one, they would have been able to add it despite the negative feedback.
Making everything proprietary and exclusive is not the only way to make money. And even if you can make more money that way, I don't care: corporations exist at the pleasure of the people, and we should feel free to demand whatever we want from them.
Even full patents only last for 20, and the "utility model" (AKA minor patent*) last 6-15 years depending on jurisdiction.