Where does one get $500k in cash? Presumably the local credit union isn't going to dole it out on request. That's why there are cashier's checks.
That is a question that I wouldn't ask. Some people deal in cash that never sees the bank or credit union. Or IRS 1040.
A few years ago I had a client that ran a local burger joint. He was buying a $65,000 house for his daughter. He came to the closing with this brown paper bag full of cash. The bottom of the bag was so soaked in hot dog grease that the cash was almost falling out. I told him I wasn't accepting 65K in cash and that he had to go get a cashier's check. He came back with about 10 cashier's checks. He had been to every bank in town.
I suppose people like that just skim a little off of the receipts each day and let it pile up. I don't know what the client with 500K was doing. And I didn't ask.