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.