Google is a Linux shop. Most Googlers don't do any development on Mac (unless they're specifically working on something that runs on Mac, like maybe Chrome). Each one has a linux desktop (or at least that was the case while I was there), and all the heavy work is done "in the cloud" anyway.
Besides iOS developers and maybe open source developers, people don't and aren't allowed to have code on their laptops at Google. You have to ssh into your desktop so presumably there's no reason to have Homebrew unless you're doing personal stuff.
There are other package managers on macOS, such as MacPorts and Fink. And you don't need to use a package manager to install software.
just asked the 6 or so coworkers here right now who have macs. not a single one has homebrew installed.