+$10,000 for a broke person is entirely different from +$10,000 for a billionaire...
I strongly agree, if it could be implemented effectively. My completely uneducated guess is that it would be difficult to obtain reliable reporting of all wealth, and that income is easier to obtain information about because it involves financial transactions, often involving banks or large corporate entities.
Taxing wealth would have other advantages. For example, a wealthy person could predict their tax liability years in advance and integrate that into financial planning. Also, I think it might avoid the claimed disincentive of high income tax rates for wealthy people: Your incentive to earn is undiminished because you'll keep 90% of the money.
In the U.S., as far as I know, there is around $85 trillion in wealth and total government budgets are around $4 trillion. On that basis, the average wealth tax rate would be under 5% per year.