Why do we pay for bitcoin in USD?

We pay for Bitcoin in USD or other fiat currencies. Does that mean the people we are paying would rather have the USD? Are we foolish to do this? No. Fiat currency is just one of the payment options. We can also get bitcoin as a gift or we can accept it as a form of payment for products and services. We can also mine for bitcoin or we can tokenise a process and create a cryptocurrency such as bitcoin.