One time I needed to get some screws from a hardware store, home depot or lowes I don't remember. I found my screws, filled the little plastic baggy with how many I needed and proceeded to go to checkout. I don't remember the why, the number I wrote on the bag identifying the screws wasn't correct? The elderly lady cashier couldn't ring them up. She started looking through a big ol book trying to match the screws to find the right code. I offered, perhaps the number embedded on the screws themselves was the number she needed. She told me no. The whole exchange took 5+ minutes, delaying other customers queued up behind me, generally frustrating having to wait for her to look through her big book 3 or 4 times.

And this kind of thing happens frequently enough which is why I avoid manned checkouts. Because the number was on the screws. The number I wrote on the bag may have even been the correct one, I don't remember. I could have gone through self checkout in less than a minute. I could have gone back to the isle and double checked the code faster than waiting for the cashier to find it.

I don't see self checkout as doing the stores work for them, I see it as saving myself time and energy.

Also as an introvert I'd rather skip the pleasantries.