Well one reason could be that you are a commercial company and you make a proprietary appliance. FreeBSD's license (3 clause BSD) is way easier in that case then the GPLv2, let alone GPLv3 (which a lot of userland is licensed in most Linux distro's). Examples of some high profile appliances running FreeBSD: Sony's Playstation 4 and Juniper's Junos OS which runs on their firewalls and routers.
Ubiquiti is getting a lot of flak for not being GPL compliant and the only thing I can think of when I hear this is: "Why did they use Linux if they wanted to make a proprietary product? They wouldn't be in this mess if they had used FreeBSD.".
Another reason could be FreeBSD ships ZFS out of the box because combining the CDDL + BSD licenses is not a problem. However GPLv2 (Linux kernel) + CDDL is a problem.