Taxes on the rich are already at European levels in the US. There simply aren’t enough of them to cover current spending.

It is a similar issue with taxing nominal wealth. 2/3 of nominal wealth in the US is completely non-liquid. Taxing the liquid fraction is essentially leveraged as a result, causing a catastrophic collapse in the value of similar investments by ordinary people as a side effect. Impoverishing a large portion of the middle class to own the rich isn’t a recipe for political success.

That the rich don't want to be taxed, obviously. and manage to convince a voting plurality that they shouldn't.

That question assumes that the current level of spending is optimal. Regardless of who pays the taxes, are we getting a good value for that spending? Or could it be drastically cut?

Laffer Curve. Depends on the country but France for example already takes 44% of their GDP as tax, runs heavy deficits, and attempts to make up the difference by increasing taxes on the wealthy causes them to leave.

At some point they'll need to do austerity.

Confiscating the wealth of all U.S. billionaires (~$8 trillion) would fund federal operations for roughly 9 months...1-time only.

After that, the money is gone.

The underlying problem of high, persistent government spending remains. This isn’t primarily a “tax the rich” problem.