Not sure what you are talking about regarding SBT. SBT does incremental builds, it's one of the few that even do this interactively. It is also built on parallel-by-default execution: The task engine runs everything that can be computed in parallel except when you request sequential processing. (Some old code-bases with broken tests for instance.)

My experience with Google software is that its usually not as good as Google employees think it is. See Go, Dart, GWT, Android, Google Groups, Angular. I think this can be partially contributed to the sect-like structure of the company where everything created at Google is the best thing ever, while everything invented in the rest of the world is discarded or ignored. See this hilarious reply from Googlers to a feature that many people take for granted, but Googlers are completely unaware of: https://github.com/bazelbuild/bazel/issues/1394

Bazel is yet another thing where Googlers think they have invented the best thing ever, and then have to realize that the world around them, which they tried to ignore so hard, has moved on since 1970, making their "really great, special tool" neither great nor special.