I'm guessing they assumed that BSD would have a lesser chance of having drivers for the hardware in their router (or if their router is ARM-based: specifically supporting the router's exact+particular system board and configuration of hardware) compared to Linux. A priori, I would make the same assumption; when I hear "router", I think "oh, that'll need OpenWrt".

For me it was mainly package management, and the unwillingness to get acquainted to a new userland.

But it has to be said, that void is pretty BSD-like, in some ways, and maybe someone will port pf one day (although I don't even know if that's possible at all...)

I was going to use either FreeBSD or OpenBSD, but no 802.11ac support in either. Actually I should have just went with it anyway. I could only get my car working in n mode and someone else who e-mailed me after finding that post said that particular Intel card doesn't work in AP mode in 802.11ac on Linux; had to buy a different card entirely.