There is almost nobody spending money in old worlds. Active players in enemy alliances consist of 1-2 players with subs of all remaining "active" accounts in their alliance.
The point is that having 10 year old worlds where nothing interesting is happening is tiresome to maintain. Especially since killing the same 1-2 players for the 20,000th time is ridiculous. Player accounts with bases destroyed tens of thousands of times continue to respawn with no real penalty, and that is ridiculous.