In the main supermarkets yes and I don't use carrier bags but when popping into an express on the way home not everyone carries a reusable bag with them everywhere they go!!
Tescos carrier bags they seem to be made out of cling film these days and always break. Also when you walk into a tesco and there are two staff standing by the self service checkouts watching you in case you need assistance. Why employ staff to watch you do their jobs for them