Bounties exist to motivate answerers, and help questions get the answers they deserve.
A few weeks ago I received my first bounty, +50 for my answer to this question. It was a two year old question, but soon after I posted my answer, NautArch put a bounty on the question. In the related banner, they said they specifically wanted to reward my answer, as it described my actual experience in implementing the suggestion. The reason for their bounty was clear, and at the time, would serve as a motivation for myself and others to write similar answers to other questions. (Now that the week has passed, I have collected the bounty but the banner is gone - it still motivates me, but it is not clear how it would motivate others no longer able to see Nautarch's intention. Regardless...)
Yesterday I received a +500 bounty for my answer to this question, an answer I wrote four months ago. The bounty is from "Community". If there was a banner listing the reason for it in the week prior, I did not see it, and I don't know how to see it now. +500 is huge - about 5% of my reputation total. Apparently the answer was well received by something or someone, but I don't see that I can know who, or why. I certainly appreciate the bounty, but am unclear on what it is supposed to motivate if I cannot know why I received it.
That particular answer was accepted, but it is by no means my only accepted answer. It received numerous upvotes, but it is not my most popular answer. It is currently my most popular accepted answer, but absent any other indication, I would hesitate to think that that is what the bounty is "for". For example, it is also my shortest accepted answer - perhaps the anonymous moderator or automated program that goes by Community has a fondness for pith?
In short, what behavior is this Community-awarded bounty supposed to be motivating, and how would I know?