As far as I understand it, AngularJS Material is used widely within Google and whenever a breaking change occurs in the repository, it also breaks Google apps and stops Google developers from being able to work. This gets highlighted very prominently and causes virtual alarms to go off.
Thus, as far as I understand it, there is a "Google pre-submit" process that is in place to verify that PRs pass all of the internal Google tests before they can be merged. Of course from an OSS project perspective, this represents a black box and an unknown since it's impossible to run those tests and verify that your fix is OK outside of Google. Unfortunately when these tests break, it's not usually the contributor who has to fix them, instead it's usually an AM core member who has to resolve the issues with the internal tests and/or PR.
As this "Google pre-submit" process is also not 100% clear to me, I can't tell you if there is some way to streamline it or not. It would be nice to hear more about that from the core team.
That said, unfortunately the current process also seems to prohibit the opening up of the OSS project to a wide range of contributors (i.e. to allow more people to perform merges of PRs). It would be nice to hear from the core team if there are any immediate or long term plans to change this?
Thank you for starting this discussion. I agree that healthy OSS projects are responsive to open issues and PRs, especially from first time contributors. I'm glad to see that there continues to be demand for improvements and bug fixes to AngularJS Material.