I believe its too easy to get to level 31 with Vanguard marks so we probably got players who just skip VoG & go straight to Crota. If that is the case, then maybe they figured it would be easier yo go backwards once you hit cap. This is something I've seen happen in MMORPGs throughout the years. Problem with this is that Destiny isn't just an MMO so people tend to mess up like that. Even if this is not the case, players should practice. Comes in handy!