I don't think it's dying in term of public. It's a niche, with a limited public, but a very dedicated public. I think the public is still there but it has reached its ceiling a long time ago.

But it's a type a game that ask for a lot of investment, and less bankable than some other online games, and a bet on the long term. Contrary to other type games, where the release is very often the peak the game, with mmo, the peak can arrive a few years after release. Most company don't have that patience.