Switching yourself is easy, but you can't expect everyone you interact with to switch too when they don't have a reason for it (and they have the same problem of getting all of their contacts to switch).
If there's interop between the chat applications - and be honest, do any of them have a unique selling point that makes them significantly better to the average user? - then that restriction is lifted.
It improves competition, which is healthy in a free economy (something corporate liberals really push for), forcing the chat apps to innovate instead of benefit off of critical mass / first mover advantage.
> Switching yourself is easy, but you can't expect everyone you interact with to switch too when they don't have a reason for it (and they have the same problem of getting all of their contacts to switch).
Sure, but "the old one is no longer available" is absolutely going to get everyone to switch in the approximately 60 seconds it takes to go from the notification to having a new account.
It's easier on Android where anyone can "become" the SMS app and integrate all your chats in one place. Apple does not allow that, so you're always going to end up going back to iMessage with some people if you just know their phone number and try to send an SMS.
For now, but that doesn't apply in the hypothetical where Apple is told "change your behaviour or stop operating in the EU", no matter which option they pick.
Switching is super hard when your primary platform just fallback to SMS.