Because nobody wants to end up looking like the Crypt Keeper.
Speaking as someone whose skin is not always in a cooperative mood, I take every opportunity I can get to improve its quality. Part of it is getting it to look nice, of course, but part of it is also not having to deal with peeling, shedding, and all those other things you probably don’t want to hear about. Remember, your skin is an organ, just like all that other stuff you got going on inside you, and like your other organs, it can be affected by the things you eat.
The first thing you want is a good source of vitamin A. Vitamin A strengthens your skin against the suns rays, kind of like a natural sunblock. Vitamin A primarily comes from protovitamin A, which is processed by beta carotene. You can get a good source of beta carotene from hearty vegetables like sweet potatoes, spinach, and, as the name may have tipped you off, carrots.
Next, omega-3 fatty acids. Don’t be deterred by the “fat” in the name, you need this stuff. Omega-3 makes your skin naturally moist, thick, and supple. Without it, you’re gonna turn into a dried-up husk. Your best sources of healthy fats are fresh fish and avocado. In addition to keeping your skin healthy, omega-3 and healthy fats help to prevent inflammation in your skin, which in turn prevents things like rashes and acne.
Finally, drink some green tea to get a healthy dose of catechin. In addition to aiding against sun damage, catechin makes your skin tougher and harder to injure. Fun fact, catechin is a major component of your fingernails, so a good supply of the stuff can also keep your cuticles smooth.
This isn’t an exhaustive list, obviously, but these foods are a good place to start. They can all fit pretty well into a balanced diet, providing important nutrients to other parts of the body, so if they keep your skin clear and healthy in the progress, who’s complaining?