P2P is harder to build and harder to monetize than client-server, so it's like poison to startups. Crackpots are still into it, but they don't give a good appearance.
"P2P is harder to build" is an equally loaded statement, though you've caught my intrigue. I wrote a WebRTC signaling server in a weekend that is capable of letting peers establish N:N connections with each other for video conferencing.
Outside of cases where TURN would have been necessary, the clients were all connected, P2P with encrypted connections. (And even with TURN, I believe end-to-end encryption could be ensured, but the traffic would go through a third party)
WebRTC makes P2P a lot easier, especially since it doesn't require installing software. I think getting peer connectivity is 10% of the problem. Video conferencing is pretty much a best case for P2P; general apps are much harder. Things like data sync and handing churn are very complex and not needed in client-server architectures.