Savagery would abound.

"They" are carrying too much cash? When do you think the government goon will put their hands on YOU, nitwit?

Since 2014, governments have taken more from the public than burglars. They are entitled to your money when it is not collected and handled as they wish.

I always wonder with cases like this of how do the police know you have that much cash on you/in the car. Traffic stops are rare, searching a car is doubly rare, carrying that much cash is rare (I think) but these happen too often to ignore. I know large bank transactions are being monitored already? makes me wonder if that info is leaked already.

Joe, here in Texas they are looking for beatup cars heading east from the casinos in Louisiana. These are small town cops with little to do all day. If you hit up a couple hundred you will find one or two winners you can take advantage of. And once you've taken all their money away they can't afford a lawyer to get it back.

The forfeiture of big sums makes the news, but the most common case is someone, usually low income, getting several hundred $ taken away. I carry that much just so I don't have to go to the bank so often.
As to "why": if you are going to buy a used car, the person will not take your check, they want cash. This could be $5000 or more easy. In other cases, people are paranoid about banks or the gov--with good reason perhaps. There is nothing illegal about carrying cash. It all originates from the drug war. If the coast guard stops a boat and it has 100lbs of cocaine and cash, the cash is guilty. But a guy driving with cash and no drugs? no