I can only speak for myself (as a developer). I try to look at all recent bugs to see if I can reproduce. If so I generally try to get them fixed. Sometimes, particularly for addons, the code is using technologies I am not familiar with, and I attempt to redirect the bug to the original author. But they don't always respond. Older bugs don't get as much attention since they are often not reproducible and are written against no-longer supported versions of Gramps.
When it comes to features, this is more problematic. To add a new feature in Gramps core, we are supposed to discuss the pros/cons in the developers list; if it seems to get some traction, then a PR is prepared by an interested developer or author. But even then, we generally have to get the approval of our benevolent dictator before it is accepted. This can take some time, witness the 'place enhancements' that have been in progress since early this year.
This is particularly true for API and GUI changes; minor enhancements can often go more easily.
Note that almost all such enhancements depend on an "interested developer or author".
Feature that can be added via addon can don't usually get as much scrutiny. As long as someone (the author) feels that the feature has some merit, and gets the code to work reasonably well so that it does what it says without crashing Gramps, one of the developers is likely to accept the PR to get it into the addons list. Of course if it later becomes problematic, and is no longer supported by the author, it may eventually get 'de-listed', although the code stays in the addons-source repository.