... It can cut both ways, and depends a lot on the 'level' of poverty and specific circumstances, although the calculus has shifted over time.
If people are working crazy hours, sometimes it's a struggle to even get time to properly shop for groceries, let alone cook. There's varying degrees of that too;
i.e. I remember the 3-4$ frozen pizzas that could be used as a dinner and leftovers; And yes, at least back then, We could instead buy some chicken, rice, and a can or two of soup or stock to do something way healthier, at the same overall cost per meal...
But it would take an hour or so to properly prepare instead of just tossing that 3-4$ frozen pizza into the oven and letting it do it's thing.
Then throw into the mix where both partners due to work and/or school aren't even home till 8PM, and one of them has to wake up by 7AM to get to work the next morning [0]
I've lived that situation, although thankfully that wasn't every night and we could balance between the healthy self cooked option and the junkish-food-pizza.
But I've also lived the situation where both parties are working late, or the commute is so bad, you're glad you advanced enough you could afford the more expensive, but at least then managable 'taco bell' option.
But then there's the sort of 'generational passing on' where we now have multiple generations raised on carry out, fast food, or microwaved meals. Sometimes where they were never given the teaching or responsibility of cooking because (for reasons similar to above, including more affluent cases) the general concept of 'a home cooked meal' becomes the exception case rather than the norm [1]
[0] - You don't want to eat too late for other health reasons of course...
[1] - And yes, that group really does tend to be less healthy overall from my personal experiences, even if their dining tastes are 'expensive'.