How does that start, anyway? What adult ever ate a chicken nugget before they had toddlers? Who keeps Kraft mac & cheese in their cupboard before they have children?
For us, it's a combination of convenience, cost and - well, expedience. Our first kid became a fussy eater but he was seriously underweight. He still is somewhere in the 3% weight range for his height and age. Thing is, telling him it's this or nothing was *FINE* with him. The kid had zero appetite, and when we saw he was LOSING weight, we tried any number of things - those expensive kid drinks with nutrients and calories (and he would spit it out), peanut butter, eggs.
Once we found he'd eat mac and cheese - he got it a lot more often. With butter. Won't eat beef but will eat nuggets and fish sticks? Works for me.
We do draw the line at drinks - no Kool-Aid. No soda. We drink bottled water. All of us.
We do pack lunches with half ready made stuff (Lunchables are really awful). But - they WILL eat it. We pay more than twice as much for a school meal that they mostly throw away.
We still have healthy choices for the kids - fresh fruits and vegetables, usually a healthy mix at dinner time. I get stuff at the produce auction and we always have summer squash and zucchini in the summertime. Wife is an outstanding cook. But we often find after a day out doing things, we come home and it's an hour to bedtime. Out come the fish sticks or instant pizza. It's not their staple, but we have three kids - it's just not possible to fit in a good meal and finish before bed time.