Yes, that is the reason that posts get ignored. There are hundreds of conversations all going on at the same time with hundreds of people contributing. There could be a dozen posts on a thread since someone last looked at it an hour ago, and typing a dozen times, "Thank you for your post XXXX, it was so interesting" and "Do you really think so, YYYY?" and "Are you new, XXXX? I don't remember seeing your user name before." could take them so long that there are a dozen more before they get to what they want to say. By then the chat has moved on to another point.
Also it is not obvious that you are new and could do with some encouragement - there are thousands of members, you could just be someone who has been posting for ages on a subject that most people on that thread don't usually read.
I think that as a new member you just have to keep putting in comments on everything you can. If you actually say "I am new to GN, so I've not seen this thread before, but I think . . ." you will be pleasantly surprised at your welcome.