Isn't that thanks to its license? They literally can be used in closed source software without a word of credit.
* https://www.freshsource.org/commits.php
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.
There's a lot of weird reasons why you'd use FreeBSD in storage appliances that I have mixed feelings about.
This is not true of any of the "acceptable licenses" listed by FreeBSD.
https://www.freebsd.org/internal/software-license/
See: the clauses saying "must reproduce/retain the above copyright".
Yeah, you will see the copyright if you are working at the company. Outsiders would never know it's a fork.
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.