I think I have figured out the reason elderly people shop at the weekend. Not that I ever thought they shouldn't - but I have wondered why, when surely the week is quieter and more pleasant.
I have figured it out by watching my mother get older.
When she has something on during the day, that is the thing she is doing that day. She can not focus on anything else but that one thing. If she has a doctors appointment at 11am, she absolutely cannot fathom going to the supermarket in the afternoon, at say, 2 or 3pm, because she has doctors that day.
My mum is only 68, and in pretty good health. Barely even retirement age.
By the time people get to, say, 80, they have slowed down even more. A poster on the first thread, before this one, mentioned that her parents don't do anything else on bin day because "we have to put the bins out". What to us is a quick chore we barely even think about, is a whole thing to them. That's their task of the day.
Everything requires more mental and physical energy.
So if Monday is a Doctors appointment, Tuesday is bin day, Wednesday is some other appointment, Thursday is the day a bill is due (which requires going into the bank because they don't do the internet and can't manage touch-dial on a phone) Friday is when the cleaner comes, that only leaves the weekend.