I think the creators you critiqued are just busy and don't lurk the forums all day (like me, lol). I sometimes get replies from messages that are months old, but i'm overjoyed to get a response. This isnt insta chat, but sometimes-active-sometimes-not kind of place.
Oh, and like Leyelle said, replying directly to a comment does not notify them. Usually they'll have to comb through the threads to see any replies, which sucks.
Use @!