Why not just use wireguard directly? The configuration is fairly trivial
Tailscale makes it simple for the user - no need to set up and maintain complex configurations, just install it, sign in with your SSO and it does everything for you. Amazing!
One value of Tailscale for a ton of simple use-cases is that people don't have time / don't want to learn.
I've seen they offer to use Mullvad as an exit node for devices which is very cool. Sadly it seems like for this to work, you have to have them manage your Mullvad keys, which to me kind of defeats the purpose of Mullvad in some ways. But I can see how it makes sense to them from a business-perspective.