Why are self-service tills in supermarkets more popular than manual ones?

Every time some supermarkets hold a festival promotion, there are always a lot of customers rush to snap up preferential goods, the shopping cart is full.  At this point, our biggest fear is the long queue at the checkout counter.  Sometimes I encountered the cashier's slow entry of goods, and the customer wanted to return something temporarily, or even add something temporarily, and let his partner go to the shelf to get something, which seriously delayed the time of waiting in the checkout line.  

Now, many shopping malls, supermarkets and even convenience stores have introduced smart means such as self-checkout checkout counters and face-swiping payment to speed up checkout.  Why are self-service registers more popular than manual ones?  

Self-service cashier is faster than manual cashier  

The self-service cashier saves customers the time of waiting in line. By pointing the bar code at the scanning box below the self-service cashier, customers can input the goods to be purchased and then pay by mobile payment. The whole process only takes 1-2 minutes if they are skilled in operation.  During the time of waiting in the manual cashier channel, the customers who use the self-service checkout counter have already finished the scanning code settlement and payment and walked out of the supermarket easily.  

Self-service cashier can optimize the personnel allocation of shopping malls and supermarkets  

Since self-service cash registers are so convenient, will self-service cash registers mean that supermarket stores will no longer need staff members?  In fact, in the supermarket's self-service cashier channel, you can see that there are still several staff on duty, they are mainly responsible for teaching customers how to use the self-service cashier for checkout.  "Self-service cashier is always a relatively new way of cashier settlement, which needs to cultivate users' habits.  Once users are familiar with the process of self-checkout, they will be more comfortable and self-checkout will be faster."  

For operators, a dozen cashiers may be too busy to handle the rush hour, requiring additional staffing costs.  However, cashiers are busy during hours when fewer people are shopping, resulting in a waste of manpower.  The self-service cash register can solve this imbalance. When busy, it can quickly collect and settle accounts to ease customer flow. When idle, it can play promotional information on the big touch screen of the self-service cash register without any manpower increase or decrease.  Self-service checkout counters can work 24 hours a day, which can make up for the lack of manpower on night shifts.