You will never understand why because you are not him and he is not you.
I know we've said this to a lot of people before, and someone told it to me a long time ago. It's a really hard concept for most parents to grasp, I think. But it's essential to letting go of your difficult child. This kind of dawned on me this morning as an easier way to apply it to them.
I like subtle foods. Sometimes I like them a little bit spicy, but only if it's supposed to be spicy, and then only a little bit. When I taste food I prefer to be able to taste several different flavors in them, like layers. I like vegetables, lightly sauted or perhaps steamed, with a little olive oil or butter, and maybe just a hint of salt or parmesan.
L likes spice. One of the best things she ever got from me was a bottle of liquid cayenne pepper from Louisiana. She used it on everything. If I had put one bite of her food in my mouth, I would be miserable. But, it doesn't make her miserable. It might give her an ulcer someday, but then again it might not. So, live and let live, I figure.
husband loves meat and potatoes. When I make shepherd's pie, I have a serving, and he has the rest. When we go to a restaurant and he orders something with a "side" dish, if the offers are "potato salad, french fries, green salad, or vegetable", he will order the french fries every time. When I make dinner, I have to tell him to put salad on his plate. If I made tater tots every day, he'd be ecstatic but I make them once a year. This is not how I'd eat. And it's not how I cook, so it's something I can control in my own home. I don't buy french fries or tater tots and we don't eat out at places that serve them unless someone else has chosen the restaurant. I would be a miserable fat gassy slob if I ate that way, and I don't think he should. So, I don't give him the opportunity to do it. But I know that he does. I give him his vitamins and fiber and I don't let it bug me. If I see that he's not putting anything green on his plate I make sure it's on the table and tell him to eat it. But I'm not him and I can't make him a veggie liker, and I won't ever understand how someone can call 'fried chicken, mashed potatoes, mac & cheese, and rolls' a meal. But some people do. It's no skin off of my nose.
I'm disabled, so I have never been a big exerciser. But, I think of it from time to time. I would like to be able to run. I have a friend who has run in over 30 marathons. Most of the year she is training. Getting up at 4:30 in the morning to run 10 miles before she goes to work. Counting every calorie she eats, and measuring every muscle. She gets pulled muscles and torn rotators, and ripped up knees. Honestly, there isn't much I could think of that I would want to get up at 4:30 to do, let alone go for a run in the rain and the dark by myself. But, she likes it. I think what she does is overdoing, but she likes it. Who am I to judge? It's no skin off my nose.
If you really need to think about why your difficult child does what he does, think about someone who likes food you don't like or does activities you would never do. It doesn't have anything to do with you, and you would see the silliness of trying to make them change their ways. It's actually none of your business. Neither are the poor choices your son is making. Unless you bring those poor choices into your house and into your life.