The clear move for Interplay is to release Fallout MMORPG in 2013 as a free to play online download MMORPG with an in game shop as a "fuck you" to Bethesda.
As for why they're doing it....
because THEY want to do it, and get all the money, or at least reserve the ability to.
Hell it's the same reason Nintendo didn't want you downloaded 20 year old NES games in the Gamecucbe era, even the really really obscure ones.








