This is common because there's probably some other, major time savings things that your wife is able to spend money on that lets her have a reliable stock of food that she can plan and prepare for her lunch.
AI or not, ordering any food delivered takes time to deal with and collect. When your food is already there, you can pick the exact second you want to eat lunch and not wait 30 or 45 minutes for someone else's delivery time frame to match yours.
Beyond time, I will go out of my way to make larger portions for leftovers because I know what's in the food I make, and I try to make healthy food. Even "healthy" options from places that deliver aren't always that healthy. There's an element of knowledge about what I eat that is equal to cost savings in my mind.
Habit + planning + preparing food in bulk can save a lot of time and money. If you're already in the kitchen preparing a Sunday evening meal, you can scale that up a bit and have a few extra lunches ready without much additional effort.