Maybe because that's the payment the seller prefers? An interesting coincidence: my bosses are rich guys. One of them collects cars. This week, preparing to attend an out-of-state auto auction, he sent his assistant to the bank to cash a large check. She came back with $30k in cash (she came in my office to show me). I don't do business this way, but if I were buying and selling large-ticket items with strangers, for immediate delivery, I want to be paid in something I believe in.
This is not to suggest that my cause is an all-cash economy; it isn't. My cause is resistance to tyranny. I reject any movement in the direction that we're all guilty till proven innocent; that it's up to us to establish the innocence of our motives, and up to us to show why we deserve to be left alone.
And if you ask her, I think you will find out she filled out a form at the bank before they would give her over $10,000 in cash. Think of that what you will.
I don't defend the law or try to justify it...I just try to explain what it is...and often I am shot because I am the messenger of news people don't want to hear.