Some of us are over 27, and have been around a while, and maybe admined on forums. It's not uncommon for posters to ask questions, and never post again. Either they got their answer and are gone, or perhaps they posted multiple places, and forgot the others when they got their answer.
I think on the internet, those who have bad behavior, or rude , or unthankful behavior, have those traits magnified by the anonymity. Whereas face to fasce, they are forced to at least show some civility, on the internet they have little repercussion for poor behavior. Especially when they have what they wanted.
But there are also those who are not used to posting on forums, and in fact, may avoid it due to personality, aversion, shyness, etc. They may just be unfamiliar with protocol. I tend to assume the latter is the case, and believe the best of people unless they prove otherwise. Hoping they got their problem solved, and are left a little better off for it. Much better to think you helped someone, even if they didn't acknowledge it