It makes sense. Returning players would be pissed off to see tokens from EDZ, Io, Titan and all of the older planets as well as vanguard and crucible deleted. The new dlc will have new maps, new NPC with planet specific gear as well as tokens that are only good for that area. As long as we have a token based system, deleting leftover tokens at release of new dlc would be a monumental mistake. That would be punishing everyone who didn't pre-order the dlc. Which would be what's known as a "dick move."