Supermarkets make money from high volumes of sales, not from large markups on items.
I posted this on a thread the other day:
"£2.3bn profits for a year. Sounds big, but think about it for more than a couple of seconds.
Over their 3,433 stores in the UK, that's £670k profit per year per store.
That's £1,835 profit per store per day.
With an average of 4,000 customers per store per day, that's 46 pence profit per customer visit.
Lets say an average customer shop of 5-10 items. About 5p-8p profit per item. The profit they make on each item is literally pennies.
Supermarkets make profit from volume of sales, not from gouging prices and having big markups on things.
If they stopped marking anything up tomorrow, you'd maybe save a tenner."