NT supports process monitoring, inspection, and alteration in a manner that's already basically a superset of ptrace. As I mentioned in another comment, I can imagine some internal resistance to adding the necessary hooks for complete support eventually making WSL1 infeasible to support --- but for social infeasibility, not technical infeasibility.

Big companies that employ lots of smart people frequently seize up and become incapable of innovating because their internal parts mesh against each other and halt the whole machine. I suspect that's what happened here.