There are tons of bugs which are easy to describe in prose, and for which such an explanation can easily allow someone familiar with the codebase to be able to

There are tons of bugs which are easy to describe in prose, and for which such an explanation can easily allow someone familiar with the codebase to be able to reproduce or even fix it right off the bat, but which would be quite difficult or even impossible to create an automated test for that could reproduce it in a way that the bug tracker could check. It might be nice for bugtrackers to offer an optional system that allows you to submit an automated test case, which could be run in some kind of sandbox, and bugs that were easily reproducible would be marked as such and could get more attention. But anything that simply discarded all other bugs would be throwing the baby out with the bathwater; you would simply not hear from your users as much, on lots of important issues.