Cash is most liquid and often untraceable, especially the cash involved in the black market, do it yourself jobs, rainy day funds in safe deposit boxes, cash under a mattress, hiring a neighbor or an illegal to do a job that is not taxed in any way, babysitting jobs, grandmas’ cash gifts, etc.
How can the government then control everything and tax everything? Remove all cash from circulation and install the CBDC (central bank digital currency) where everything will have to be approved and paid for by electronic transfer by appointed bankers each time a transaction is requested.
Working for the government, the banks would tell you what to eat, how much to eat, when, what to purchase, where and when you can go on vacation, what to do with your money, how much money you can keep, what car to buy, how much money you can withdraw, if you are allowed to buy gasoline, a car, a house, tickets for a show, have TV, heat, air conditioning, food, go to doctor, buy medicine, buy a plane ticket, anything that keeps you alive and well as long as you behave according to government dictates, you obey them, and your social scoring is good.