* library maintainers must make sure they don't introduce any regressions to any users at all. There's no major version number that you can increment to let people know that something has changed. Development necessarily slows.
* Library users must deal with any breakage in any library they use. Breakage can happen at any time because everybody effectively builds from HEAD. There are complicated systems in place for tracking ranges of bad CL numbers
Monorepo isn't entirely to blame for this, but it certainly doesn't help. I've been at Google 15 years and I'm tired of this.