Consider that you have $70k/yr in living expenses, and many people don't even come anywhere close to earning $70k/yr.
Food is one of the places you can cut a lot of your spending without needing to make major lifestyle changes, so it's one of the first places people look.
Also, I think you will find different people place different value on food flavor. I personally am very, very deep into "eat to live" territory, and I take a certain amount of pride in that approach.
Cut out the cars and he's down to $50k/yr. Though it can be a social disadvantage to varying degrees, it is possibly to live without a car in most urban areas in Australia. Still $20/day per a person is much higher than average. It's possible to cut down on that quite a lot and still enjoy nice food. Then again, it might be these people who will spend anything who are pushing the food prices up here. Food inflation has been rather significant in Australia in recent years (it's still at least a percentage point higher than general CPI). Though probably also a result of the duopoly held by Woolworths and Coles.
Food is one of the places you can cut a lot of your spending without needing to make major lifestyle changes, so it's one of the first places people look.
Also, I think you will find different people place different value on food flavor. I personally am very, very deep into "eat to live" territory, and I take a certain amount of pride in that approach.