To me, the strongest motivation for Bazel arrives with a complex (slow) build spanning multiple technology ecosystems. Bazel does a great job building all of them, without privileging one over all the others. It has all the key features you'd expect, dependency graph control, caching, distributed computation, etc. You can add support for whatever local complexities invariably arise with custom rules.

The Java ecosystem has much of that available also though - even a large Java-only project is somewhat tough to justify moving away from the tools almost every developer will arrive already knowing.