That's a good question.
I'd say it's because chans are just so damn slow, nobody likes waiting around for some rando to come and answer a thread that got posted three days earlier.
>  >Be me
>  >Be on some random social media
>  >Post a thing, wait five minutes.
>  >Six hundred answers! 
>  >Be me.
>  >Be on some random chan.
>  >Post something
>  >Come back three weeks later.
>  >Still no responses