I never worked at Google, but based on my experience elsewhere it is partly security and partly standardization of guaranteed minimum functionality.
For example, security aside, as an engineer working on X that depends on internal tools Y, Z and W, I do not particularly care what variant of Linux is under the hood as long as I can run my favorite WM, editor and user apps. But I do want support on Y, Z and W if they misbehave. If I run a non-standard OS or distro I will likely get a lukewarm support because those teams will put debugging problems in "non-standard configurations" as a low priority.
Personally, I learned to live with most Linux distros. When I did roll out a non-standard setup I had a standby system in a standard configuration that I can show failures on before asking for help. My 2c.
For example, security aside, as an engineer working on X that depends on internal tools Y, Z and W, I do not particularly care what variant of Linux is under the hood as long as I can run my favorite WM, editor and user apps. But I do want support on Y, Z and W if they misbehave. If I run a non-standard OS or distro I will likely get a lukewarm support because those teams will put debugging problems in "non-standard configurations" as a low priority.
Personally, I learned to live with most Linux distros. When I did roll out a non-standard setup I had a standby system in a standard configuration that I can show failures on before asking for help. My 2c.