The game doesn't keep releasing new expansions in the hopes that new players will join. They make expansions for their existing remaining playerbase and to make some of the veterans who left the game come back.
I played this game for 7 years from 1999 and I'm pretty convinced this is still the best mmo to ever grace our computers. The problem is the graphics.. as that will always be the problem with a 10 year old game. If this game had a means of updating the graphics engine beyond small texture tweaking then it would be getting new players because of its immense sea of content alone.