If you have enough issues, just deduping and knowing when a commit fixes an issue to remember to close it becomes a problem.

Not saying this is an excuse, but it's unfortunate reality that "close most issues, see which ones come back" is one of the easier ways to focus on the most important bugs

Well, unless they have a triage team, you're counting on developers having a Spidey-sense that there's an open issue related to what they're working on. I assume the issue list is something they never asked for but feel obligated to doing a minimal amount to clean up.