I've read that the notion of picky eating kids was nurtured by the food companies of the 50s in the US.
I completely believe it since they've done it as long as I can remember. There's a particularly foul one right now with a young mom chasing a kid with a forkful of broccoli (good luck with that little turd when he reaches his teens)
And gullible parents buy into it and serve mac and cheese all the time.
And kids learn that they are allowed to fuss over food.