[jedberg]

This is probably the best argument: Familiarity.

However, we're talking about very specific needs: super high performance networking. If you have that specific of a need, wouldn't you want something unfamiliar if it solves the problem best?

[jebblue]

If it's truly better and the only difference is remove Linux and install BSD then what is BSD doing that is better/different/messed up that the packets can flow faster in BSD than in Linux?

[Matumio]

Talking about unfamiliarity and specific needs: FPGAs are much better suited than CPUs for processing minimum-sized frames at wirespeed. They can still forward all unhandled frames to a CPU. Yes, it's a lot of development effort compared to a CPU-only solution, but considering all the kernel-optimizing-multicore-cleverness from OP I would say we are approaching the break-even point.