Not to mention that self-hosting/federation comes with a million small headaches.
If the devs are paid, do you want to pay them to work on the project or work on maintaining a contact infrastructure?
If they aren’t paid, do you want them using what little free time they have working on the app or working on maintaining a communications network?
If it’s someone else’s forum/matrix/chat server, are you okay with 1. a third party having access to your communications and 2. being able to force a comms blackout for any reason whatsoever?
Or would you rather they use their time and money focusing on finding a provider who meets every need of the project AND every user?