No need to ask, what happens for those 0$ waggering. The tournament is not ended yet, and most the time few hours before tournament ended or few mins before ended. Someone will boost waggering of their account.
Siince they opted in for the contest, then they will most likely start participating actively sooner or later. As you said, in such contests, some participants prefer to wait until the last moments to become active.
I don’t think we will need to wait for the last minutes, though, as there are already only three members on the top 20 who haven’t made any wager yet and we are more than nine days away from the contest’s end date.