Sorry, I can't tell you why, I don't see a reason why I would downvote that. I understand that hurts, as they have a bit of power behind them. Your post still has a not-too-bad reward though, so keep going! Don't think about it too much, this is the internet and some people are dorks. Maybe they thought it's overrewarded, maybe it was a mistake and they thought you would have bought votes (which you didn't, or curangel wouldn't have voted), maybe they counter upvotes of specific accounts (which can be for several reasons not connected to you or your post at all), but does it really matter? You don't ask for reasons for upvotes, do you?
Embrace the mindset that nothing is yours until the payout is done, it's a lot easier to accept that way.
It's not directly beneficial, but also not bad for the platform, because the rewards are given to other authors.