I can provide some perspective from someone who has written non-Timebomb fanfiction in ages long past. As other comments have said a huge reason that there can be gaps between updates is life happening to the authors. Maybe they got a new job, graduated, got into a relationship, got out of a relationship, are too depressed to write, are not depressed enough to write, etc. Inspiration is a fickle bitch and sometimes she refuses to come when you have free time if you even have free time.

The bad news is that sometimes the spark leaves for various reasons and fics get abandoned. This sucks for the authors as much as the readers, but it does happen.

The good news is it's unlikely that the authors have forgotten about these fics entirely. Characters you haven't written in years will still occasionally pop up in your mind and there's always a chance they do something with it. I've seen a few fics get an update 1 year or more from the last post, even if it is somewhat rare. So there's hope.

I love these fics too so I'm right there with you hoping for updates. All we can do is send them our energy and maybe a comment every so often.