They didn't wait, there was proof of the Reddit admins doing it in the past, manipulating votes on r/The_Donald, Altering Comments, Removing Posts, Un-Deleting comments to make it look like the mods weren't doing anything. You name it the Reddit admins manipulated the Databases to do it without traces.

Edit: As for waiting until now they haven't, they just wanted to wait for a hole, the first threat wasn't the Admins and then the others were, the Admins waited for one that got deleted, they undeleted that one, then replied and rallied the violence themselves, in turn making it look like the Mods were doing nothing and make it look like there were more users advocating violence then there actually was.