For one thing, Uk companies are not the only people running retail outlets here.
For another, imho, lofty morals & the bigger picture will not put food on the table of a normal working class family, or indeed one which has suffered job loss, this week. There are many families running on a very tight budget week to week, to ask them to spend more than they have to on patriotic grounds is both churlish & unrealistic.
And for yet another, the supervalues & local supermarkets have suddenly been able to source produce at better prices & pass these onto customers. There can be little doubt that prices have come down, special offers abound. So why weren't they charging those prices 6 months ago? Little wonder the populace feel little loyalty towards them.