Linux and the BSDs take APIs one from the other all of the time. The issue with having a Linux ABI is that you don't need just the few APIs you're missing, you need to implement the WHOLE Linux API and it has to be _perfect_, otherwise stuff will randomly break. I loved the original WSL, I had to use it for a time period back in the day when I was stuck on a Windows PC, but it can't be denied it was full of random bugs