RE: Why did a post telling people to report bugs make 3,000 USD in upvotes and my actual post about a legitimate security issue that the developers directly thanked me get less than 100 USD?

I'll restate in my own words the comments from @limitless and @suchnewb that I completely agree with. Votes come from the audience. The size of the audience will, in general, decide the size of the payout. The audience for a technical bug report post is relatively small.

Posting rewards are not a bug bounty. If one is desired, it should be administered a different way.

However, you did learn another lesson with this post (currently earning $6500 as I write this), which is that by making valid and technically interesting bug reports, and then blogging about it, you become more relevant to a wider audience, leading to larger rewards.