Sadly it's for this reason that I won't be a GM of RPs anymore. The amount of effort I put into making some RPs only to have it fall apart after a short time just isn't worth it.

I think part of it is also what I will call action and reaction posters. There are some people out there that will respond to an event that someone else has created, thus making it so that they won't post until something has happened. So if you happen to have too many people that are waiting for something to happen... well, nothing ends up happening. :P
[hider=Example]
Player 1: Opens door and enters into room
Player 2: Follows player 1 into room
Player 1: Encounters monster and fights
Player 2: Also fights monster
Player 1: Kills monster and is injured
Player 2: Ask "Are you ok?"

So, best example I could give, player 2 is reacting to what has been thrown at them, and thus player 1 is 'always' trying to drive the story.[/hider]