Most players tell another if there is a problem and if it cannot be resolved then 'game over'.
As others have said, some are fly by nights, they use the site for a short while and then wander off on their way, it may be because the site isn't really for them, it may be because of other outside influences.
What is infuriating is when there is a playing constantly online, but they have not told people that either their game needs to go 'on hold' or that they have lost interest.
There can be another reason for this.
It could be just something as simple as they haven't realsied you have replied and are sitting looking at you being on line and thinking the same thing.
I use the Show new replies to your posts. link at the top to check my games and sometimes they don't appear as a replied topic, so I ask any who are in a game with me to PM me if I haven't replied in a reasonable amount of time.
Send them a PM and say "Hi, have you missed my reply in our game or is there a problem?"