>>> I do not believe their target populations are particularly representative of the overall population
If you want to see the figures broken down by age groups, social groupings or regions, see here:
https://docs.cdn.yougov.com/rb8h1x3cog/YouGov%20-%20Supermarket%20switching%20cost%20of%20living.pdf
Tesco have never really known which audience to target their sales at. Aldi and Lidl have always been 'low price but with limited range' supermarkets. Asda has long been the lowest-priced 'full range' supermarket. Waitrose's big selling point has always been its top quality products, with Sainsbury's seeking to be a sort of 'poor man's Waitrose'. Morrisons big selling point has probably been its specialist food counters (fishmonger, butcher, baker, salad bar, rotisserie counter, etc) and its relatively low prices in comparison to Sainsbury's. Tesco, on the other hand, has long been 'just another supermarket', with nothing particularly special to draw customers to its aisles.