This still make no sense, even bad developer can’t wait week for the price of an addon to be possibly 10$ lower and there is a very limited satisfaction and effect to post negative question.
Technically, it’s pretty straightforward to block Q&A for new accounts with no purchases or to automatically clean up Q&A from accounts that didn’t buy the addon after a week. I’ve managed several big forums before, and there are tons of automated ways to clean up bots, spam, or negative behavior without affecting real users. It’s even easier when purchases are involved.