Right... but this will be an anchor on adoption. I can see why e.g. the Android build system does the same thing since it's all off in its own world anyway. I doubt you'd be popular with Linux distro packagers if you required bazel for some C library.
We realize that not everyone wants to check in all of their dependencies, and that's cool too. Check out the build encyclopedia for rules to talk to 'plain http' and maven repositories.