Tailscale uses Wireguard, but offers so much more on top. I used to think the same, but I think I was mixing it up with Zerotier; had a play with it and now think it's pretty great.
For example, you can set ACL rules for which devices can access which others (or the internet, if you have explicit exit nodes) - it's using Wireguard for networking, but you can't do that with (just) Wireguard, it's not just 'make Wireguard easier to set up', as you said that doesn't really need doing.
There's value to some to having networking config centralised like that. It allows things like auto adding certain clients to certain rules/groups automatically.
Not spending time cycling through each server to poke iptables.
For example, you can set ACL rules for which devices can access which others (or the internet, if you have explicit exit nodes) - it's using Wireguard for networking, but you can't do that with (just) Wireguard, it's not just 'make Wireguard easier to set up', as you said that doesn't really need doing.