I perceive the checkout kiosks as "the fast lane". Which gets invalidated if people with a full cart block them. Plus, the probability of something going wrong

I perceive the checkout kiosks as "the fast lane". Which gets invalidated if people with a full cart block them. Plus, the probability of something going wrong and them needing assistance is about 25% per item, with many items it's a sure thing they will need assistance and block the queue for a long time.