I'd say we don't know unless we ask Netflix engineers but the comments about license look like a good one to me. Then there is in my opinion the "bloated" Linux versus the more clean BSD experience (I am a Linux user and I like to tinker with BSD sometimes). Maybe it is still true that BSD will not run on as much hardware as Linux does but have you ever compiled a custom kernel on BSD and compared it to compiling a custom kernel on Linux ? On BSD it is in comparison much easier and the documentation is usually really good.