This is a bad reason to stay on a WL. But if you follow this to the next step, this person gets an offer, declines it, and then the school is onto another WL applicant. The school is the loser, not other people’s on the WL.
Personally. I think as an applicant, you should decline all WL offers that you would not accept if offered. If you committed to your #3 school, stay on the WL for #1 and #2. Hearing from #6, having to respond, and give it mind share is just kind of a mess for everyone