To track bugs.
The Test devs do read the reports, but don’t work on every bug reported. And some reported “bugs” aren’t actually bugs.
They also, on occasion request additional info from users in order to reproduce a certain bug themselves. A bug that isn’t reproducible is very hard to fix. The prioritization of the bugs are also based on severity etc.
From the Bug report forum guidelines:
While you may not see me post here very often, please know that your reports are read and appreciated. In the event that the amount of information in a bug report proves to be insufficient during our investigation, you will see me ask for additional information (like your hardware configuration or what time you encountered a specific issue)—so keep an eye out!