Not that there are any other options. You're not gonna run datacenters on Mac boxes or Window s, nor would you want to pay a Unix vendor
... but Google solves the "A Linux fleet requires investment to maintain" problem by investing. They maintain their own in-house distro.
Not really, it is just a well known outside distro plus internal CI servers to make sure that newly updated packages don't break things. Also some internal tools, of course.
It's downstream of Ubuntu (unless that's changed) but it's tweaked in the ways you've noted (trying to remember if they also maintain their own package mirrors or if they trust apt to fetch from public repositories; that's a detail I no longer recall).
In 2018, Google replaced Goobuntu with gLinux, a Linux distribution based on Debian Testing
Well FreeBSD exists, just look at Netflix