Possibly Canonical prefers to spend its effort developing components which aren't in the rather small set Greg checked? Things the users can actually see? Things like, oh, GNOME? (Or KDE, I suppose, although Ubuntu isn't KDE-focussed.)
The Linux kernel and infrastructural stuff is very nice, but not everyone who uses it as a basis needs to enhance it, nor is there anything immoral or unethical about choosing to enhance non-infrastructural components instead.