I suspect fear of liability for people getting sick eating expired food, plus the cost of managing it, are more of a deterrent. Legislation / govt. advice making it clear that the shop won’t be liable would help, but there would also need to be legislation pushing them to absorb the costs of distribution. It might sound like a fairly simple thing to manage, but on top of the costs of having some space for the food, cleaning and throwing out spoiled items there is the issue of managing people. People can be quite horrible and anti-social, so you can expect there will be things like people throwing things they don’t want on the floor, tasting and spitting out food and getting into fights over who gets what - the possibility of getting something free seems to bring the worst out of some people.

I am incredibly lucky and have three distribution points within walking distance for food waste from various local bakeries and supermarkets, and it is a great resource but not everyone is grateful for it.