Spoilage if you don't eat it fast, which is part of the convenience factor you mention. Harder to protect fresh fruit & veggies from pests, than anything in a sealed package, which I think is a factor that doesn't get enough attention. And the smell of them will attract more pests. Once you're out of precious fridge space, assuming your fridge is well-functioning and its seals are intact enough to keep pests out, you'll need extra, reusable containers that seal to protect anything else... which can lead to even faster spoilage, with lots of fruits and veggies.

Meanwhile, the store-brand pop tarts can deliver 2,000 calories/day for like $3, and come with sealed-per-serving packaging. Sure, they'll give you diabetes and malnutrition, but....