USD is the world currency and that's why it is used. It would be tedious and expensive to have markets in many different currencies.
As for transferring money around, paypal is one of the best options when using just one currency. I personally have used previous and still use a service called transferwise to save money on fees when converting funds from one currency to another.
If you exchange one currency to another they fix some exchanging fees so you should not in all time. But cryptocurrency have own growth so it will move to forward or backward. I personally supporting to crypto economy because Fiat currencies are totally scam so government only earn more profit not for common people.
I'm well aware of the fees for transferring one currency to the other but some times it is necessary if you're moving from one country to the next. Crypto is not ideal for this because the fees combined buying and selling end up being more expensive unless you're transferring large amounts. I neglected to mention that mostly lately I just use revolut, that's not for moving my fiat but it allows me not to need to transfer funds to different accounts and different currencies. I can have one GBP account but spend in near every currency with no or limited fees.