So your dad will only shop at Sainsburys despite having an Asda on the doorstep?
I don't get going to a supermarket at all. We've had groceries delivered once or twice a week from Sainsburys, Ocada, Tesco, Asda, etc for about 10 years.
The concept of walking around a supermarket on a regular basis fills me with dread - all that wasted time and effort.
There are, of course, other supermarkets much closer (2 within walking distance) but they are not quite so big, have a limited choice and are situated in areas which attract a certain class of clientel (known in the UK as Chavs). For him, the inconvenience is worth it - although it does take 3 hours out of my day.