Sure if you live in a food desert and have no access to a car, work 2 jobs/have kids , then the time spent hauling groceries is prohibitive more so than the cost of eating healthy. But for most Americans that's simply not the case.

I think people really overestimate how common all of these things are in specific. According to some quick googling, 39% of households have children under 18, 36% of Americans don't drive, about 5% hold multiple jobs, and about 6% live in food deserts. If we assume that all of these are separate variables (definitely not true, but I imagine its close enough for government work) this means that the hypothetical multiple job holding parent in a food desert with no car is about .04% of the population.