I think the problem with btrfs is that it entered the spotlight way to early. With Wayland there was time to work on a lot of the kinks before everyone started seriously switching.
On btrfs a bunch of people switched blindly and then lost data. This caused many to have a bad impression of btrfs. These days it is significantly better but because there was so much fear there is less attention paid to it and it is less widely used.
Fam, my experience was one (1) (uno) year ago. And during those five years Wayland made zero progress by itself - it was everyone else who had to do the job of Wayland for free.