"Food deserts" (areas with no access to fresh food) are a huge problem, yeah.
Also, economically struggling people often can't prepare their own food, even if given groceries for free: they may be physically disabled, they may be unhoused, they may be unable to afford utilities or appliances, etc.
However, I think that altering the offerings of fast-food restaurants is not even remotely a suitable way to address that.
Given that full service grocery store access is area-income dependent in the US, it's a complicated situation.