That has been around since the 1980's to make it harder for drug dealers to spend profits. Any deposit, or withdrawal of cash over $9,999 is reported to the feds. Anyone buying a house, car, boat, plane etc. with over $9,999 cash money has to be reported too and results in an investigation. It can be less if the bank employees are suspicious. For example multiple $5000 withdrawals over a few months.
I don't understand why anyone would do this anyway. It'd be so much simpler to just have the bank make out a certified check to the seller. There is more paperwork involved at the bank to withdraw the $10K in cash than to have a check made out. You have to do each withdrawal $10K at a time and fill out paperwork on each withdrawal.