One of the usual goals of a democracy is equal representation ("one person, one vote"). You can transfer your representation to someone else - either directly, in the sense of proxy voting, or indirectly, in the sense of voting for a representative - but you don't give it up permanently. When elections next happen (and if elections don't regularly happen, it's not a democracy), you get your vote back and can freely choose what to do with it, again. If your representative isn't doing what you want, you can choose another one.
That's not true of the system of money. Even if it were theoretically been true at some point, once you transfer money to someone else, the associated power of that money stays with them or whoever they choose to transfer it to. If you bought Windows 95 for $209.95 a quarter century ago, that fraction of your ability to "vote" on how society values things left you a quarter century ago, after spending it exactly once on valuing Windows 95, and it probably never returned to you (unless you became a Microsoft employee or supplier).
So, someone who makes something that is (rightly or wrongly) highly valued thereby accumulates the ability to value things in the future, and have disproportionate influence on what is then going to be highly valued. This process repeats continuously and has repeated for centuries.
More simply, the US Constitution was not approved by "one person, one vote", not even with a dozen caveats and asterisks.
One person, one vote is certainly gameable. One dollar, one vote is even more so.
All modern democracies are representative. People themselves don't decide about things, their representatives do. This is the price we are willing to pay to get effective governance.