Blizzard has realised that since they sell name changes, allowing people a richer pool of names to buy from makes very good business sense.
This idea probably came from what I assume have been extensive brainstorming sessions with the goal of finding any (cheap) changes they can make to the live game to distract players from the fact that it hasn't been updated in a year.
Or even more cynically, maybe they thought of it last year and have been keeping it in their pocket for just such a need. Hmm... would they delay the money train just so they have something to do during a slow subscription period? More active players means more purchases, right?
It strikes me as a very Farmvillian tactic; the wealth of ex-WoW players are now being dealt the news that an aspect of their character will degrade if they don't return in time-- the obvious goal being to galvanise ex-players into returning if they were on the fence.
Is this the first time that this has happened? Leaving characters the way the player left them has been a long-standing tradition for this game, and it's easy to understand why (sunk cost bias). Even deleting a toon has never been permanant.
Cynicism aside, I wonder whether this might geniunely be the best time to release unused names, in the same way that this is the best time to recruit reliable raiders: Less committed players tend to have stopped playing by now.
I'm more inclined to believe the cynical explanation though.
I've been raiding with a new 10-man group. We spent last night wiping our way through two boss kills, which isn't incredible, but being in a slower group did put me at the top of the healing numbers, which I think probably does more for my reputation in the guild overall than trying to put out good numbers against their best healers while learning a progression fight. Never underestimate the power of looking good.