That's not how the site operates. You're not voting on the price of items "for your benefit", you're voting based on the evidence provided, or lack thereof. What you want means jack squat; the site is based on market trends, not someone's opinion. If someone suggests a price, and no one is buying or selling them anywhere near that price, why should we change it?

As for why owning one is a problem? That's owner's bias. It goes back to what I said about someone's opinion; in this case, the owner is trying to raise the value of their own items for personal gain, usually without any sort of proof that this should be the price. Again, this site is not built on personal opinion. It's built to make an accurate account of what the prices of items are.

This site does not accept pricing based on the voting score; it is the admins that ultimately decide whether a price is accepted or not. This means that they scroll through countless trades on outpost checking whether a suggestion is correct or not. Voting just allows the admins a way to see whether people generally agree or disagree with a decision, but in the end plays a very little role in the acceptance process. That is why voting for benefits, instead of whether a price suggestion is correct or not, is unnecessary because it does nothing, but lose you contribution points.