You will need to ask Bernie to be sure but here are some ideas:

Although, you won´t get your money back and will be ignored, if you want to promote something that already has an upvote ( I tested that, too )

You can't vote for the same post twice so this makes sense and the account doesn't make any claims for giving individual support for people who make mistakes.

It's a pitty that he seems to care more about the money than about the content, but who really cares.

Don't think this is very fair given all the community initiatives he has supported with his own money but it seems doing good deeds generally goes unnoticed.

I hope that this randowhale project is kind of a honeypot created by @berniesanders / @engagement to find out all you greedy little ones, to flag you down into oblivion with his full power, when the time is over to counteract the flag.

Sounds like a conspiracy theory.