Very few communication services are truly P2P; it's way more likely to have syncing issues and is virtually impossible without at least a handshake. Even Signal, which does have syncing issues due to being mostly P2P, requires a server for the initial handshake.
Especially on mobile, where you want to conserve battery life.
Each person only uploading one copy of video in a multiparty situation is a huge win for quality on mediocre connections.
Skype used to be "P2P" where one party would act as the host in a group call.
True for audio, not video.
IIRC, this was because of a lawsuit with VirnetX.
It never was (or only was for a short period) thanks to patent trolls.
P2P calls and video calls are patented. I don’t think anyone offers them anymore since the Virnetx cases.
Even for completely P2P things, you can still have server-driven feature flag, which Apple definitely makes extensive use of.