I attribute most of this to iMessage and the associated lock-in effect. You don't see the same trend in the rest of the world where 3rd party messengers (Whatsapp, Viber, Line, snapchat, etc) are mostly used for comms. The inability of iPhones to easily host 'cracked' apps also acts as an anchor to adoption - theres a lot of people hooked on their cracked ad-free spotify or youtube apps, or games with 'everything fre…
I wouldn't want to be part of the team having a deadline of March to develop and implement a way for every big messaging app to interoperate, with different user models, privacy concerns (e2e?), data storage models, data durability models, etc.
Yet if it launches late, you have that 10% of revenue fine hanging over you, which is huuuuuuge. And the EU probably won't listen to you when you say "we implemented this API but their API was incompatible with ours".