For much the same reason most people choose Windows or Mac over Gentoo. Most people set up something like Tailscale to accomplish something rather than create a project and ongoing maintenance burden for themselves, and setting up Wireguard is not terribly friendly to the uninitiated.
WireGuard is one of the easiest things to set up. The total amount of reading you'd need to do to set up WireGuard amounts to half of a page. I spent more time figuring out what firewall rules are needed for WireGuard traffic than actually setting up WireGuard, it's so simple.
I'm going to disagree with you there. It's been a while since I set up anything with WireGuard but "easy" is not a word I would apply to it. A simple tunnel or VPN configuration was close to that but a network comparable to a Tailnet got pretty involved to do properly. By contrast Tailscale was effortless.
Needing to do additional things like figure out firewall rules is exactly what I'm talking about. I enjoy tinkering for fun most of the time but I'm generally looking to tinker on something specific, not every step along the way.
AI has mostly removed the difficulty of Linux configuration for beginners
It's also removed the difficulty of configuring a mikrotik router as well. Mikrotik has a cloud router instance which is much easier to deal with I think than linux. Mostly because there's a UI interface for Mikrotik that makes it a little easier to inspect what's going on.
One of my pet projects I need to get back to is an SDN to make configuration for mikrotik routers easier (particularly with VLAN's, wireguard or VPNS, or routing configuration between ports).
Winbox is nice in a sense because it tells you the true configuration. But what I really want is something that can start with a network diagram (e.g.) and then get the current state of the router, and then validate that against the network config.