It there was fraud invoved, one party may get damage/compensation.. But forcing someone to provide service is just not right.
(With the exception of monopolies of course. Let's regulate them.)
I currently have an Inbox of multiple messages from family members awaiting me, except I refuse to log into Facebook to view them. The only remaining notification email I have left enabled for Facebook is exactly that -- private messages. This way I can contact the relevant person elsewhere and ask them what the message was. This is the kind of "bending over backwards" I have to do to avoid the surveillance-capitalism crap I'm coerced towards by these platforms that can do essentially whatever they want AND demand exactly how we are _allowed_ to interact with them. Why can't I use an unofficial Facebook Messenger client and read the <100 bytes of communication my family member wanted to send me? Ahh yes I have to agree to a hundred-page ToS and subject myself to ads and privacy-invading user tracking to see those few bytes. This is fine.
Why should the first party be serving content to people using third party apps that generate them no revenue? Just like websites are free to block adblock users, app apis should be free to block third party app users.