It’s a promotional thing. They get to “get into the holiday spirit” with themed packaging and commercials. The current “American Santa” is basically the 1930s Coke advertising Santa.
Actually it goes back a bit father than that.
From Wikipedia: "One of the first artists to define Santa Claus's modern image was Thomas Nast, an American cartoonist of the 19th century. In 1863, a picture of Santa illustrated by Nast appeared in Harper's Weekly."
Here is an image from 1881: