Because there are only so many hours in a day?
Open the process up to everyone in Known Space, and most of the feedback you get will be useless.
Select a group of reviewers that you know are competent to test the candidate release, and you get better input and a far better chance of getting the release worked through in a reasonable amount of time, with a reasonable expectation of success.
And yes, I've dealt with this sort of thing in hardware development over the past 30 years.
The worst part is you end up getting more feature requests than identified bugs and the average person is useless for reporting problems in any way that resemble meaningful.
"MY COMPUTER DOESN'T WORK AFTER UPGRADE!"
"Can you be more specific."
"Yah. I guess. My computer doesn't 'function' now."
"Gee, thanks."