In my opinion, I think people prefer to use cash than Bitcoin because it's convenient and easy to use. Buying and selling food, goods daily with Bitcoin will be a little bit difficult because not everyone knows how to use Bitcoin to trade, and not every industry accepts Bitcoin. For cash is different, people use it easily to buy, sell, exchange, everyone knows how to use cash. And if you say they do not cost money, that's not true, both ATMs and credit cards need a fee
That's because we have a system built around fiat currency, and it makes sense that it's more convenient to use fiat because that's literally how the world economy regulates itself. If we had an economy built around Bitcoin and fiat was the "new thing" then we would find it to be more convenient to purchase things in Bitcoin rather than cash.
However, if you pay with cash, you don't have to pay fees.
You are right, the global monetary system was built around fiat currencies - by the way, they never saw Bitcoin and other cryptocurrencies coming. If it were the other way round or even on a level playground, the fiat currencies would by now taken their places in the museum.
As for not paying fees when we pay cash, I guess it depends on what is being paid for. With some items and services, sales tax or valued added tax is paid implicitly. That is one of the reasons most governments are grumbling over Bitcoin.
