To me (As an outside observer) the reason for the status change seemed pretty clear. There was no activity on the issue for a month and a half, and then someone made a new comment that personally attacked a google employee by name as a bad faith actor. Of course google is going to shut that down real quick.
They closed the ticket 12 minutes after that comment. It seems unlikely a coincidence. If someone wanted a reason to shut this down that comment gave them all the ammunition they needed. Don't forget, Google is not a singular entity and is made up of individuals with differing opinions, some of which are pro and some against jpegxl, but like any human social group, if you cause them to feel that one of their own is being attacked they are almost certain to close ranks.