That's not the same thing. Those services cost extra. If you go to the store and take home the things yourself, you're avoiding paying the extra fee for those services
Another example: self-service gas pumps.
Thing is: even a person that does self-checkout quite often is still much slower than a cashier, who has 100x more practice. Also, when anything goes wrong with self-checkout you typically need to wait for someone to get to you and fix the issue - cashiers typically are able to fix their errors themselves.
So, in the end the lines will be longer, because of less skilled people doing the work.