In the first chart does the "rewarded" bit mean the number of contributions that have been rewarded at the time of posting, or does it include contributions that could still be rewarded (are currently in the queue)?

As for the reason(s) behind the low number of contributions... I think it could be a combination of everything, haha. I don't think the suggestions category is affected by the new bot (unlike development and translations), so if people are confused about it and not contributing to the suggestions category, then that is a shame. I would actually say this is a great time to submit suggestions, because there isn't much competition, if any, so it probably means your suggestion will be upvoted in the next voting round every time.

From what I can tell (I could be completely wrong) it's pretty difficult to get a suggestions contribution "accepted" because of a multitude of reasons. It doesn't really make sense to me to be so strict with a category like this. Maybe lowering the maximum voting cap and lowering the reviewing standards will help with that, as that will allow simple, but still valuable ideas to also get submitted.

Anyway, I really hope it comes back to life, as I always appreciate hearing ideas from others about my own projects!