that solution is not trivial because it requires permission for anyone to comment on issues, which invites irrelevant or unhelpful comments or even complaints. the separation allows issues to be limited to developers only, those who actually work to fix the issues.

technically, messages are messages. this approach no more than grouping messages into different forums. it could also all be under discussion with a sub forum for issues, one for features, one for other topics, etc, and then there would need to be a permission system for each sub forum.

so all this does is to create two spheres of access for users and developers. and that's the point.

in the end it's really a matter of taste and preference.

That's not true, you can limit comments to collaborators if you don't like them. Although note that it's something you've made up, comments are not part of the original list of reasons. Moreover, comments aren't limited in the actual issues, so nothing prevents unhelpful comments, leaving your issue unresolved