it's quite disappointing to see one-time posters all the time
The question you need to ask is what is disappointing?
One I suppose is that, well they only post once. Well that thing called free will gets in the way there. Sure we would like them back but I;d rather they do it willingly.
Another would be the fact of repetitiveness. You know those where is my xbox emulator posts. Well I personally call that spam, so good riddens.
I guess a third would be, the way of thinking its cutter, but after all, regardless of the fact they made one post, they still contribute to the forums. So its not all that bad.
So what is the reason you bring it up?