"Europe" covers too many countries and supermarkets to make such a generalisation, I feel. In Estonia at our local supermarket the self-checkout lanes / machines are often extremely busy, and also introduce the chance of getting stuck behind a number of people who have problems using the machine or who are just slow.

We know who are the fastest operators at the 'manual' check-out, and it's easier to watch prices as they are scanned when one doesn't also need to be doing the scanning.