It can be very hard to eat a healthy diet if you're poor or if you live in a food desert, or you have a dietary restriction, or some allergies...

And it becomes even harder when you mix any of those two criteria, let alone more. Then factor in your environment. It is way easier to eat healthily in Italy than in the US. (Maybe that is what you meant with Food desert.)

I disagree on the “if you’re poor”. I find eating healthy cheaper.

You can prepare healthy meals from basic and cheap foodstuffs like vegetables, whole grains and legumes, eggs, low cost meat cuts etc. You can prepare delicious meals for under $1 each.

Buying prepared unhealthy foods is what is expensive.