They don't have a choice, they cannot encounter a good vegetables and fruits in the normal stores. They CANNOT, at least in the UK. It's that simple. Maybe during some events, as a curiosity.
Good quality vegetables are not available on the shelves in general. Maybe in some cases, yeah. Some. But generally not. Similarly with meat, although it's much easier here to find something decent.
The difference in taste and quality between the cheapest and most expensive fresh fruits and vegetables in the supermarkets is virtually none. If you don't believe me, you don't have to, I simply grew plenty of that as a kid and a teenager, I keep growing some, and the difference between the average garden-sourced (or PYO/small farm sourced) and the Aldi/M&S/Waitrose/Tesco is simply too big to describe, you'd have to try it.
So there's an illusion of choice between awful and bad - in that case I'm simply choosing imported (thanks to the landfill and manufacturing waste in our great British food chain). People who don't know, or don't care pick whatever looks the best.
Some buy the cheapest. Not everyone buys the cheapest - you can't seriously claim that in case of the expensive stores (Sainsbury's, M&S, Waitrose).
And then there's palate problem. If someone was raised on these garbage produce, they may even favour it over healthy, proper ones. Proper radish will have a bite to it. Proper tomato has a complex profile (and there's hundreds of varieties of that too), instead of how garden stores describe it being "tasty"....
Consumers have been dumbed down and trained into accepting inferior livestock feed as food, and thanks for that they can for example say with a straight face that they actually like or prefer Tesco white toast bread.
(they've been scammed)