I really think this is part of it.

I had to learn how to cook when I moved out because I never learned from my parents (to their credit, they tried, I just didn't want to learn). It wasn't hard necessarily, there's plenty of good resources, but it's a bit of a learning cliff. When you decide to cook your first "chicken breast and steamed vegetables" style healthy meal, you don't just have to buy chicken and vegetables. You need to buy your seasonings, you need a pan, you need a meat thermometer, you need a pot and a steamer basket, etc. Once you have these things it's easy to use the same tools to cook a pork chop the next night, then salmon, then soup, etc, etc, but that first step is almost overwhelming if you don't already have a history and culture of cooking.

And then once you're past the learning cliff, there's still a learning curve as you get a feeling for which spices work with each other, how to combine cooking methods, gathering a baseline of recipes that use the same ingredients so you can have more variety without waste, etc. It's a useful skill, and one with plentiful resources, but if you're time poor and stressed it always seems easier to just use Grubhub as your personal chef and swear you'll get back on the healthy eating train... tomorrow.