Tailscale is an abstraction layer built on top of Wireguard. It handles things like assigning IP addresses, sharing public kegs, and building a mesh network without you having to do any manual work. People like easy solutions, which is why it's popular.

To manually build a mesh with Wireguard, every node needs to have every other node listed as a peer in their config. I've done this manually before, or you could automate it (eg using Ansible or a tool specifically for Wireguard meshes). With Tailscale, you just log in using one of their client apps, and everything just works automatically.