Most people use checks or credit cards for big purchases. Most people are paid by check, and the exceptions are usually near minimum wage.
Nobody does big transactions in cash anymore -- even if you want to pay tens or hundreds of thousands in cash for a car, a house, or college tuition, if you show up with a briefcase full of cash, then your counterparty will tell you to put it in a bank and come back with a check because they're not set up to handle cash on their end.
Government policies are designed to encourage inflation, yet the government stopped printing $500 and larger bills in 1945 and has never continued them.
Most of the people who were old enough to remember the Great Depression and hoarded cash throughout their lives because of their experiences are old enough to be dead or in an old folks' home, and their hoards of cash have already been deposited in the banking system by their families. Living through the Depression hasn't been a "mainstream" experience for many decades, and the actions of those who did have been dismissed as "silly, irrational things that old people do."
Basically it's become so abnormal to have large amounts of cash that a lot of people agree with the government -- "if you're using a lot of cash, that's so abnormal, you must be involved in something illegal." It's so abnormal it activates our tribal instincts which cause us to de-humanize -- "That's not something that I would do, or anyone I know would do" -- it's much easier to accept the demonization of people who use cash.
Of course, this is just how the government and big business wants things to work -- all those bank deposits and credit cards are much easier to track. Think about all the junk mail you get based on your credit rating -- the marketing departments in those companies love the amount of information you're giving away about your finances.