1. Islam and some fundamental Christian denominations prohibit dealing with those who do usury, so some people can't use banks.
2. One could just have sold a car for cash.
3. People lend money to each other and the chef could just have been paid back.
4. Some people believe in reptiloids, some believe in imminent collapse of the society, so they buy bitcoin, dig bunkers and store cash in safe boxes.
5. Some people may want to store money in a place which is out of reach of their ex-spouses.
My point being: big pile of cash is a bad excuse for a search.