1. This is an MMORPG, which are known for being never-ending. Simply giving us a storyline will make it end.
2. Everyone does the story then moves on. If there is nothing waiting for them when they finish the story then the game is beaten and you move on to the next one. That isn't what MMORPGs are about.
3. If you don't like what Square Enix is doing here then why don't you leave? Nobody likes an asshole.