I think cryptocurrency as a currency is still (yes, I'm saying this in 2022) a neat idea that I hope eventually gets working well enough to go mainstream.
First off currency, unlike investments, need to be somewhat stable. The price of things and services cannot fluctuate by significant margins in days or weeks, so it is not a good currency.
Secondly, It is extremely resource intensive. We spend too much money on too many things for every translation to take that much energy. If is takes more energy to process a transaction for a cup of coffey that it took to make the coffey, it is not a good currency.
Thirdly, it is too public. Everyone's purchase history probably should not be public knowledge.
Also just legally. I watched an interview on some stablecoin once, and then read a little about it. I am pretty sure they are breaking millions of laws every hour. Law enforcement are slow to understand new technology, but they eventually catch on, and our societies are not going to throw out all of our finance laws just to allow crypto currency to exist.