I don't think it's reasonable to expect every single thread to get a reply. I think that's pretty standard across all forums on the web.
It's just not always possible or reasonable to help someone. Often people post threads where it's nearly impossible to help. For example if they post with little more information than "my project doesn't work, please help", what can anyone say to that? You could try to help anyway, but it shifts all of the burden of work on to whoever tries to help. It's kind of lazy from the poster since they haven't bothered to provide any useful information or read our guidelines on how to best get help, forcing whoever tries to help to take them through that guide step-by-step, which is all extra work on top of actually helping. It's in their own interest to provide good information anyway, since it makes it more likely their problem can be solved.
It's like your car breaking down, phoning up a mechanic, just saying "my car's broken, fix it", then hanging up. If it's a quiet day they might phone you back and ask a long list of questions to try to figure out what's going on. If it's a busy day they might just shrug and leave you to figure out that you need to be more helpful yourself next time.
So I wouldn't trouble yourself with trying to reply to every single thread - even just new ones. I think it's totally unrealistic. I used to try myself back when the forums were quieter, but it was pretty hopeless even then, and now the volume is so high that I only step in where I think I can quickly provide something useful based on the information already provided.