Sadly, I think that most casual pet owners (not fanatical dog and cat lovers, just, you know, those slightly apathetic people who have a dog) have absolutely no idea what a really healthy animal looks like. It doesn't even occur to people that it could be the food causing their animal to look bad, or that food could make a difference.
I know I posted this story before, but it's relevant, so I'll tell it again. When I got Nadja she had been on that sort of low quality dog food, probably for her whole life. (She's ten.) Her skin was dry and more flaky than you can possibly imagine, her fur was thin (honestly, she looked like she was balding in spots), greasy, and coming out in huge clumps, her teeth were yellow, her breath smelled, her skin smelled, her fur smelled, her poops were gigantic and stinky, she had no muscle tone, and she wobbled when she moved. Did I mention how bad she smelled? I mean, when you petted her, you had to go wash your hands afterwards, because you would get all stinky and greasy. And that's just what you can see on the outside of the dog! I wonder what the inside of her looks like.
Anyway. I put her on a quality kibble (Wellness) and added olive oil to every meal for a while, and within, hmm, about three weeks, she was beginning to look -- and smell -- a whole lot better. Her gigantic flakes of dandruff began to get smaller and smaller, the hotspots on her skin healed up, her fur grew back in thick and soft and luscious, and she started getting muscle tone, which helped her move somewhat better. The only change that we made was her diet, so it's obvious that it was simply the food that made the difference.
I now feed a mixture of BARF, home-cooked, and quality kibble, and she looks -- and smells! -- like a new dog. Her teeth have even gotten whiter, from the raw meaty bones.
If someone is feeding a low-quality food, I guess they just get used to the results from it, and assume that they are normal and that dogs are just naturally stinky and sheddy and have rotten breath and yellowed teeth and horrible gas and that's just the way it is. Many people just have no idea that it could be any different, or that the food could be causing those symptoms.
Since you're going to start Harley out on a quality food, you'll hopefully never see this first hand! But if you ever get in a rescue who's in bad shape, and you change the diet, you'll absolutely be able to see the change. Why aren't the companies going out of business? Because they provide a cheap and easy product and advertise so heavily that their product is more well-known and readily available than any other, they pay for veterinary nutrition classes, and people are reluctant to change, particularly when the change ends up costing them more.
Man, I am long-winded.