If most Americans want this, why can't we have it?
Because it's illegal?
How can you tax someone for something they actually haven't earned as income?
Example: Some gazillionaire has say $50 million in stock in a company they started. The stock grew in worth from $10 million to where it is now. No different from you and me owing a home and it appreciated in value.
Now, if the government comes and says to that person, you made $40 million and we're taking $20 million in taxes on your earnings even though those are only on paper, they're taxing unearned wealth.
Worse, the gazillionaire decides that taking that hit is too much and unfair. So, he dumps the stock at a loss, say for $10 million causing a panic in the market and the company to crash economically. This results in his declaring a loss on it and no tax paid. Then, in the next tax cycle he buys back the stock for $10 million, recovers the company's position only to do it again in a year to avoid the taxes...
The people who think this law will work are fools. The gazillionaires are not stupid. They got where they are by being smart. They'll figure a way around an onerous tax and fuck the government out of that money to the harm of the economy--but to their benefit.
The Left is full of idiots for thinking otherwise.