Any systems level team will prefer this form of tightly integrated solution to the systems layer problem if they are responsible for the highly built out specialized distributed application we call netflix. The reasons for design choices going all the way back to freebsd 1 are available on the mailing list in a central place. Everything is there.
Trying to maintain your own linux distro is insanely difficult, infact google still uses a 2.2 kernel with all custom back ported updates of the last 30 years.
The resources to match the relatively small freebsd design and implementation team are minuscule compared to the infinite crawl of linuxes, a team of 10 freebsd sysprogs is basically the same amount of people responsible for designing and building the entire thing.
It comes down to the sources of truth. In the world of fbsd that's the single fbsd repo and the single mailing list. For a linux, that could be thousands of sources of truth across hundreds of platforms.