Frequency, part of it is my own (DH and DD make their own, different, lunches, for example, and I hate to eat in the mornings so make the smoothie the night before while they both start slower and eat cereal for breakfast).
But the stir fry dinners is family food. Part of it is because I grow some veg, and usually only have small amounts of a few things at a time to use. Or I'm using bits of things from the fridge. And as DD is fussy, she will eat some of a mix but may not eat anything if it's a single veg dinner. I usually slice and dice the next type of veg to throw in while the first one is cooking in the pan/pot, so it doesnt' take much extra time really.
And I do a big bag of medditteranean veggies on occasion - courgette, onions, garlic, tomatoes, peppers, mushrooms, maybe beans (aubergines if only me to eat it) - all diced up and seasoned, and then thrown into the oven to roast (or skewered for BBQs in summer) or frozen raw. Leftovers freeze well and make a great base for tomato sauce and pasta dinners, or reheated as a side dish. Add some chicken, bacon pieces, chopped sausages or prawns - and dinner is done. Or leave out the meat/fish for veggie nights/guests. I started that by accident when I had a couple of courgettes and peppers looking past their best, to avoid just throwing them out - and now that's a staple in my repertoire.
The smoothie, I know, is a first world solution.
But I get a LOT of my veg either from the garden, the local greengrocer (cheap one - the posh one's veg is not that nice!), or Lidl, so it's not as expensive as it seems. Fruit is greengrocer or Lidl mostly (except for work stuff for me - I go into M&S near the office for that rather than carrying so much on the train along with lunchbox, laptop and work papers etc). So can be a lot cheaper than meat a lot of the time.