Cash isn't easy to trace. We have contractors here that only deal in cash. They don't even like to run checks through their bank. Some don't even use a bank. I recently paid a contractor in cash because he didn't have a bank account in order to cash a check. I don't have a problem with that because it isn't my job to keep track of his business transactions using my bank account. Cash, or Federal Reserve Notes is legal tender for all debts, public and private.
I think many people these days think a person is doing something illegal by using cash. I gave a Costco checker some cash the other day because my bank card didn't work. She gave me a dirty look.
Personally I still like the idea of cash and keep some in my safe. When the EMP bomb goes off I'll have a way to buy some food and fuel. OK boomer.