Yeah, most shops that are still open have reduced their opening hours. Always best to check them online before you shop.

There are lots of reasons for this:
- reserving certain hours of the day for NHS workers or elderly people
- needing more hours in the evenings to restock shelves which are stripped bare during the day
- staff shortages due to workers being ill / self-isolating / looking after kids and others

It's unhelpful in some ways, as you say, but I understand why they're doing it.