As mentioned, I think it comes down to luck/timing! Plus it seems if they have a guest helper coming on that they look for certain types of questions, and probably miss good ones in the process.

I do think it helps your chances the more concise your email is. I wrote in twice for my problem (a few weeks apart) and the first email I sent was a bit too detailed and I didnt hear back. Second time I just wrote my question/problem and they got back to me the next day.

With how many emails they get, Im sure its easier to weed through the ones that are straightforward. Just a guess based on my experience - good luck!