[yupsurprise]

Yes, each of the big techs has teams that just work on the build systems, however it should also be noted that none of the big tech use the open source Bazel, Google uses Blaze internally which is what Bazel is derived from, Amazon uses Brazil which has nothing to do with Bazel and Meta uses Buck, which I know nothing of so I won't comment on it.

The major issue I found when trying to use Bazel was that its essentially a build system without specific rules for each language, hence rules support for each specific language is dependant on each language's specific community, most of which are quite tiny, and mostly maintained by upstreaming changes from their individual companies, servicing their own needs, hence a lot of work is required to make it work for your own company's needs.