People with lower body fat have a harder time regulating their bod temperature. Body fat is for storing heat, so those that are skinny will get colder faster and more often.
Lol EVERYBODY can get cold. But if you're asking why skinny people are colder than fatter people, that's not true. Skinny people have higher metabolism while less body fat as insulation so it evens out. I don't know about you but I'm really skinny and wears a tank top in 60 degrees weather with no problem :D
Because they are too skinny and they don't eat and balance thier diet