It works transparently with any project using autotools/cmake/meson. (which is 95% of open source projects, and most likely most enterprise software) No need to convert your project to starlark BUILD files.
Not only it's distributed like distcc, Bazel also provide sandboxing to ensure that environment factors does not affect the build/test results. This might not mean much for smaller use cases, but at scale with different compiler toolchains targeting different OS and CPU Architecture, the sandbox helps a ton in keeping your build result accurate so that it could be cached remotely (like using ccache).
On top of it, the APIs Bazel uses to communicate with the remote execution environment is standardized and adopted by other build tools with multiple server implementation to match it. Looking into https://github.com/bazelbuild/remote-apis/#clients, you could see big players are involved: Meta, Twitter, Chromium project, Bloomberg while there are commercial supports for some server implementations.
Finally, on top of C/C++, Bazel also supports these remote compilation / remote test execution for Go, Java, Rust, JS/TS etc... Which matters a lot for many enterprise users.
Disclaimer: I work for https://www.buildbuddy.io/ which provides one of the remote execution server implementation and I am a contributor to Bazel.
But it has protobufs interfaces (IIRC), so a distributed build farm would generate the grpc endpoints for their implementation and then you tell bazel on the command line (or via .bazelrc) the address of the build farm it can use.
I doubt that it is the main feature. RBE is difficult to deploy and consequently rarely used. On the other hand of you assume that 99% of bazel invocations are done by google, then weighted that way RBE is nearly universal.