Maybe they choose the nicer groceries because eating is the only thing they have left in their life to look forward to? Since having children, home ownership, and retirement are all off the table in terms of affordability? Idk, just spitballin.
No one said that we're buying processed garbage instead of vegetables.
If vegetables, beans and rice is the core foundation of your diet, then any money you spend on processed snacks is a splurge, because it's not necessary but you enjoy it.
Depending on the time of year, produce is what I splurge on.
In winter, I get sick of apples and satsumas, I could spend $4 on a highly processed snack that is tasty but doesn't offer much else, I could $8 on a relatively "healthy" sweet snack (compared to the cheap snack), or I could spend $8 on small scale greenhouse grown strawberries.
Given my options, if I've got money, I'm going to buy the strawberries, which is a splurge considering apples were $3 and there's nothing wrong with apples other than "I'm bored of them"