Porting SDL doesn't mean you significantly change the portable codebase of it, you simply add another target.
That's the whole point of being a cross-platform toolkit.
Also, the reason why porting of different toolkits in general seems to be somewhat stagnant is simply what Wayland hasn't reached 1.0 yet,
and so it doesn't really make sense to port against an unstable protocol which might change and thus much porting hours would simply be wasted.
If I was to voluntary invest my free time so that other people could use my work while likely never saying thanks anyway,
I'd at least try to keep the amount of wasted work to a minimum.