That's an unfortunate pendulum swing cleaning up from their problem of yester-year - namely, bugs sitting around _forever_ without any comment.

I noticed they changed that policy when I started getting comments on years-old bugs of closed-obsolete. If they're now 90d expiring bugs, I'd _guess_ there's a bit that can be set for your account of whether you're a customer paying for support, and that their support staff have a queue filter that prioritizes those, and the rest get expired if nobody comments.