> It's actually terribly expensive compared to a bag of rice and potatoes

What about the time cost?

To make food from fresh, you need significantly more time to prepare and cook the ingredients. You also need more frequent shopping trips to ensure fresh food is ready for cooking.

If you're working long hours or working shifts, or are living on your own, this becomes significant.

Also of course rice and potatoes on their own are not very nutritious. Brown rice is better than white rice, but that takes longer to prepare again.

Preparing a meal from fresh also takes more willpower and energy than selecting more immediately available calories. I'm pretty sure that's a lot easier after coming home from an office job rather than a 12-hour factory shift.