It's not really a problem because they don't want people joining the tracker in general. It's about accountability, exclusivity and the quality of the user base. Invites being for sale means any random person could join, hindering the exclusivity and likely the quality of the userbase (a good user is already in other trackers and could join with other means). And of course, it also means that the user who bought the invite is more likely to break the golden rules because them getting tree banned is of no concern to them.
From the staff's POV it is very much a problem and some trackers are famous to drop the hammer at the slightest violation of the golden rules.
From the staff's POV it is very much a problem and some trackers are famous to drop the hammer at the slightest violation of the golden rules.