It's a mix of licensing and performance/stability. The licensing ensures that a company can implement their own IP and not have to contribute that back to the community as open source.

The performance/stability of FreeBSD is no joke, that's why, as mentioned previously, storage vendors like Isilon and Netapp choose FreeBSD as the base. They can contribute upstream when needed, but they don't have to provide any source for how their storage appliance software.

https://freebsdfoundation.org/testimonial/isilon/ https://freebsdfoundation.org/end-user-stories/