Tailscale does use Wireguard, but it establishes connections between each of your devices, in many cases these will be direct connections even if the devices in question are behind NAT or firewalls. Not every use-case benefits from this over a more traditional hub and spoke VPN model, but for those that do, it would be much more complicated to roll your own version of this. The built-in access controls are also something you could roll your own version of on top of Wireguard, but certainly not as easily as Tailscale makes it.

There's also a third major "feature" that is really just an amalgamation of everything Tailscale builds in and how it's intended to be used, which is that your network works and looks the same even as devices move around if you fully set up your environment to be Tailscale based. Again not everyone needs this, but it can be useful for those that do, and it's not something you get from vanilla Wireguard without additional effort.