There's nothing about Wayland that ties it to Linux. Wayland compositors tend to require a few features exposed by the graphics drivers (e.g. DRM) but there's nothing stopping the BSDS adding these (iirc FreeBSD already does).
at least FreeBSD does already have Wayland. It has a few more hiccups and rough edges than on Linux (at least from my PoV on running it on an older laptop) but otherwise it works fine.
You wouldn't pick BSDs for a desktop anyway, assuming you want a working system and don't want to use Windows/macOS.
Now the concept of a "working system" can be a bit hard to grasp for some people, so let me put it this way: There are vastly more things that normal people do on their computer that work on Linux than on BSDs.
