On any large team your compiler should be checked into revision control or have a way to fetch a specific artifact & have that pointer checked in. That way you're guaranteeing everyone is using the right thing.
Because in general yes, I agree, it would be nice. Probably not in source control though -- putting in compilers + libraries will make checkouts very slow, git is not really designed for tens of gigabytes of stuff.
For bazel specifically, this is not really well supported. The default rules and all examples just trust system-installed compilers.
There is ongoing work on building in docker (with all the corresponding security issues), and there are rumors that Google internal version has some sort of magic, but this is not a "mainstream" configuration.
However, I think my point still stands -- this work looks pretty experimental. And most tutorials, including bazel's own [0], recommend using default configuration, which uses system compiler. And most of the examples I have seen also rely on system compiler.
[0] https://docs.bazel.build/versions/master/tutorial/cpp.html
This is because configuring a checked-in toolchain in Bazel needs tremendous effort and very specific knowledge about something 99.9% of developers does not know and DOES NOT WANT to know or spend their time on.