From an outsider point of view it looks like the ecosystem would have been much healthier if KDE and Gnome had used wlroots. Get everyone talking in the abstraction so plugins can be written.
Whereas Wayland originated in 2008, sway didn't exist until 2015, Wlroots 2017. This is not when they were ready merely when development begun.
Furthermore it was of vital import for KDE and Gnome to support both X11 and Wayland for years and leverage their large existing codebase. Wlroots would both have to travel back in time like the terminator from 2018/2020 to 2010 and become universally suitable en route.
Have you looked into it? I believe writing a wlroots compositor to be in the general ballpark of as difficult as writing an Xorg window manager—which is, beyond the type of project I’m likely to take up in my spare time, but at least doable by mere mortals.
Far more work. I wrote the X wm I'm currently using in a couple of weeks and it's a few hundred lines of code. You can get a working X WM in a few dozen lines or tens of thousands. Mine is ca. 700 at this point (floating+tiling).
I considered wlroots but the complexity is far higher and Im not in a rush to move to Wayland.
Furthermore it was of vital import for KDE and Gnome to support both X11 and Wayland for years and leverage their large existing codebase. Wlroots would both have to travel back in time like the terminator from 2018/2020 to 2010 and become universally suitable en route.