Most of this was successfully done 20 years ago by tinc, which is a project written by a couple of European guys in their free time. It even supports routing traffic through other peers and does peer discovery just like BitTorrent (but before BitTorrent even existed) — there is no need for a central server.
What tailscale has over it is hype, lots and lots of hype. Also a much more well thought out, and arguably more secure VPN protocol underneath, which is why GP's comment is on point.
If it's hype, it's not hype the way you're thinking. I've shown Tailscale to a lot of people (this is less salient now, when pretty much everybody uses Tailscale) and the most common reaction I've gotten is "holy shit". It is spooky simple to get working, and it's spooky simple to go from a working installation to a VPN configuration that would take many many hours to replicate with pre-existing tools.
There may be VPN nerds out there who think there's nothing special happening with Tailscale, but I submit those nerds haven't spent a lot of time dealing with the median, replacement-level VPN configuration prior to Tailscale. I'm a pentester, and so I have had that pleasure. Tailscale is revolutionary compared to what it replaced.
Because you're delegating the control plane to Tailscale. Somehow we went decades without this being a thing for security reasons, dealt with the management of VPN appliances, and now suddenly everyone is OK with Tailscale owning the control plane of their VPN for the sake of convenience.
For a company this is probably okay: companies rely on other companies all the time, and can enforce contracts. I would gladly use tailscale at my company.
For an individual, heck no. Fortunately, headscale exists for individuals to use.
My only technical complaint with Tailscale is that its hole punching doesn't seem to work with some common CGNATs/double NATs when both endpoints are using them, and then traffic ends up trickling through their public proxy servers, while running your own is kinda annoying and not recommended or documented.
What tailscale has over it is hype, lots and lots of hype. Also a much more well thought out, and arguably more secure VPN protocol underneath, which is why GP's comment is on point.