The code cannot enforce no self votes or spreading votes, as there will always be ways to get around that for malicious actors.
That's why we have downvotes. Don't see it as war we wage against you. It's a form of pushing you into the right direction. The hope is not that you disappear, but that you start honoring the concept of Proof of Brain.

It is basically good to support others and grow, but in practice, this is impossible because the source of money (Steem) is limited.

So because it is limited, you should get as much as possible, without thinking about all the others? Great way to build value and attract new users!

If you have one kilogram of gold then you can give 100 gr per 10 people, or 100 people per 10 gr etc.

The big difference is that when you give away gold, you don't have it yourself any more. Rewarding others with your votes doesn't cost you anything. And to make it more attractive, curation rewards have been raised by 100%! Still not enough for you to go out of your way.

And for the posts you feel are overrated: use your downvotes on them! That's what they are for!