Do you think that people that create posts they think are crap should flag themselves?

Well, they won't.

They commonly self vote, and purchase votes, to gain rewards, because most people won't upvote crap.

If you find your posts are undervalued by the market, then either you are a poor judge of post quality, according to the market, or the market is out of whack, or both.

Either way, when you self upvote your posts, you are associating yourself with those scammers by emulating what they do.