I think part of the reason is battle-testing. Blaze (the Google internal version of Bazel) has been used by 20k people per day for well over five years to conti

I think part of the reason is battle-testing. Blaze (the Google internal version of Bazel) has been used by 20k people per day for well over five years to continually build a single mammoth shared C++, Java, Python, Shell (plus others) code base complete with a globally distributed cache system and thousands if not tens of thousands of build machines.