When I ignore a comment left here at LW, this is sometimes for the reason I often ignore comments sent to me by email. The reason is this. Upon first encountering a comment, I may not feel motivated enough to compose a reply, and as a consequence procrastinate on it for a while. After enough time has elapsed such that I feel motivated to write the reply, I feel that I must include, in that reply, an explanation to my correspondent of why my reply took longer than expected. Knowing that my reply must now include this explanation itself demotivates me further, and causes me to procrastinate even more. This gives rise to a perverse cycle. The longer I postpone my reply, the more elaborate I feel my excuse must be and the harder it is for me to write it. The cycle is usually broken only after a few weeks. At that point the excuse I feel I ought to write is so complex and enough time has elapsed that I become convinced I will never write it, so I simply write the original reply either abstaining from offering any excuse at all, or prefacing it with a very simple, formulaic apology like "I'm sorry for the long delay."
Must your reply include an explanation or apology? It seems to me like you're torturing yourself a bit over something most people wouldn't worry too much about. I'd just post what I was going to post. People are busy & posting things on the Internet is typically pretty low priority. At least, that is my default assumption.
I often feel guilty for ignoring other people's comments or questions, and frustrated when other people seem to be ignoring me. If I can't indicate to someone exactly why I'm not answering, or can't receive such an indication myself, I can at least help my future selves and others obtain a better probability distribution over such reasons. To that end, I'm listing all of the reasons I can think of for someone to not respond to a comment/question, to save the effort of regenerating these hypotheses from scratch each time and prevent the possibility of failing to consider the actual reason. Note that these are not meant to be mutually exclusive.
If I missed any reasons (that happen often enough to be worth including in this list), please give them in the comments. See also this related comment.