Yeah, AFAIR the basic realization at some point was that most freely submitted user reports were either of low quality, part of something that wasn't on the near-term roadmap, or part of something to be addressed more broadly in the near term anyway, so the value of them got lower over time. It kind of happens in every FOSS project to some extent; early on in a project's life, user feedback is almost always useful to help hone your direction and future scope, but at a certain point, that value diminishes once you know the contours of what your users want, competitors do, what timeline you can complete them in, etc. Phabricator and its vision were very stable. Evan at some point moved to a support-only model IIRC because he didn't believe the value versus support burden justified the alternative anymore.
(And actually, you could still submit bugs and comments generally speaking if you were an "old school" contributor who had generally high-value contributions; I was in this category and never had my permissions pulled, and dropped by from time to time to submit things -- but that was the exception and not the rule.)
