Because those aren't peer-to-peer in reality. They're peer-to-peer in terms of a virtual network that's often (not necessarily, but certainly in this case) implemented using a central server anyway.

Those are peer to peer. The coordination server manages the public keys, and exchanges the ip addresses initially. After that peers connect directly.

Relays are involved only briefly initially.

How is Tailscale not P2P? Just because there's a central server for discovery and key exchange does not somehow make it not peer-to-peer.

If the actual communications between two clients is P2P then, by definition, the VPN is P2P. Because that's the actual part people are talking about when they talk about VPNs.