There isn't much special secret sauce that Netflix has at the OS layer of things, so there's not much reason for them to keep the patches in-house (and then have to maintain as the public source rolls forward). Other vendors that give back are Dell EMC Isilon (keeping their OneFS code private), Juniper, Netgate, etc.
Sony is unique in that it was a one-time fork, and now that the product is out there's not much churn in things.
Most vendors have learned that keeping things in-house just causes pain down the road when you have to re-base with the latest FreeBSD release.
If you're fine with violating the license, then there is nothing stopping you from closing the source to GPL licensed software without a word of credit. I'm not sure what your point is.
Being available alongside Linux distributions as official supported OS on major cloud vendors.
Maybe the contributions to upstream could be better, but that is the choice they decided to make.