I don't understand this. Rather than pay a (yet to be proposed)
higher capital gains tax, Americans would pull their money out of the markets
right now and put it into what? Is the plan to make no capital gains in the future?!

Exactly. Why sell and pay more than 50% tax in some states (43.4% in TX) on above 400k (or is it a mil)?
The position that you don't have to sell is further solidified by this.
I wouldn't like to pay 50% on what came from holdling through blood, sweat and tears and I
legally wouldn't have to if I DON'T SELL.
For some, like Bawb, it is too late as they will make it retroactive to Jan 1, 2021, no doubt (it it passes).
A big boost to all btc lending services. However, if your btc collateral is liquidated, then you would have to pay cap gains taxes:
https://www.forbes.com/sites/shehanchandrasekera/2021/03/17/how-are-crypto-loans-taxedOf course, there could be even more wicked scheme about yearly taxation of unrealized gains, but i would deal with that when it materializes.