Another reason is that USD is deeply intertwined with fossil fuel production and trade.

99.9 % of the cryptocurrency space is bullshit but in the remainder there are some viable alternatives to state issued currencies. Unfortunately difficult to discuss due to the prevalence of bullshit, and easy to criticise to make yourself look smart & moral while defending the status quo.

maybe it’s possible to make a coin that’s worth 0 USD but can be exchanged like USD

Hard to imagine how would that work, I guess if you can use it to purchase, you can use it to exchange w/ USD. And then you get the business types who tend to ruin everything. Maybe very small local currencies could kinda work that way? Chaumian e-cash mints, like GNU Taler & others.