First valid reason is property rights. It's your money, so you have right to carry it in any place, in any form, however you wish.
Money can be used to buy stuff. It can be used to buy vegetables, fruits, meats, coffee, gold bars, guns, automobiles, houses, or crack cocaine. That's the #1 reason to carry cash. You go with the cash into vendor's shop, or even lemonade stand on the street and you can buy anything you wish, because it's your money.
Money can be used to buy services. You can use it to get a haircut, to fix the roof, to buy a training, or to buy sexual services. While some governments will object to your god-given right to pay services in cash, or make businesses register you as a cash holder, buying services is still a legitimate use of cash.
Also you may want to carry money around to show off. Just like peacocks carry their heavy ornamental tails, you may want to carry a roll of dollars around your neck. And even though it may make people jealous, inadequate, or even violent and possessive about your wealth, it's still your right to show off your wealth. Even if only to mark your skills and superiority, you have rights to parade with cash, and to say it otherwise in case of theft or civil forfeiture would be victim-blaming.
Finally, cash is resistant to electricity outages and network failures. Your ATM may not work if there's no radio link to the bank, and your shopowner may struggle to accept your debit card if there's no electricity. With cash payments, everything works, money can be calculated on paper without electricity. So this is your additional right, you can do legitimate business even when big systems do fail, because you use a paper rather than bits.
Another good reason for using cash are bank fees, and negative interest rates. If it's costly to keep money in the bank, you can as well live without a bank. Preferably also hold multiple hard currencies, in case your country's economy goes to hell.