I have to assume most Linux WiFi drivers are written by people working for companies who get to see documentation via NDA as part of a company project OR the driver was written by the manufacturer who already knows how to talk to the card.
So everyone else has to cargo cult those drivers by blindly copying the voodoo code and hope it initializes the card the same way it does in Linux. Someone suggested adding a driver compatibility layer to allow using FreeBSD drivers in 9front but the devs shot it down with "that layer would be bigger than the kernel itself" So now you're now responsible for maintaining that HUGE mess plus you're still dealing with black box drivers you hope someone else fixes when they don't work. No one wins.
Again, the damn hardware manufactures have to give us proper hardware documentation. Until then they can go suck an egg.
Some cards work perfectly by copying OpenBSD drivers or have some documentation. Though many cards require cargo culting by copying undocumented behavior from undocumented Linux drivers in order to get the cards working. The big problem with that approach are issues which arise cant be debuged. Best they can do is poke around and guess.
This whole thing is the fault of hardware manufactures.