FreeBSD (and other BSDs) are also a much simpler platform with orders of magnitude less "churn" taking place - if you are doing an engineering experiment that involves low-level integration with OS-level or kernel-level subsystems (eg kernel TLS f.ex) then it's a lot simpler to start from BSD, and you can very safely assume that your code will pretty much continue working in future releases as well. It's a far more stable platform to build a product around, Linux is "constantly on fire all the time" in comparison to the absolutely sedate pace of BSD development. It was built over the last 50 years (the oldest code in the FreeBSD repos dates to 1979) and it mostly Just Works Like You'd Expect. The good old 'cathedral vs the bazaar' tradeoff. Well, if you are building an annex, at least you know the cathedral isn't going to collapse under you next week, and by the time you get your project finished the bazaar might have moved on to something completely different and abandoned the thing you needed. But you don't get docker and the other New Things either.
Sony likes it because it allows them to release proprietary software off an open codebase. The conceptual divide is - GPL protects end user freedoms, at the cost of developer freedoms (eg linking to code with GPL-incompatible licenses, or not distributing the source to proprietary extensions to a GPL'd product). While BSD/MIT license it's the other way around, they're "here's this code, you can use it however you want", and sometimes that means doing things that users might consider "evil".
The reason companies like Sony and Apple pick FreeBSD is because they get an open source POSIX-compliant OS they can drastically modify down to the kernel level without having to open source their modifications.
Who knows what plans Netflix had in mind when this decision was made? Maybe they simply commit to FreeBSD because they do not want to release their code under the GPL. I certainly never do, and I will never ever make any improvements to any GPL code I use. I think it is an awful license. Maybe Netflix does, too? That would be directly relevant to the license of the OS even if they never release their customized OS, if they have a customized version at all.