Anti-Fit is one of the characterising features of the 501 Levi’s Jeans and been with the jeans since 1890. It’s a way of cutting the rise of the Jean in a straight line and not contrary to curving, which gives the 501 distinguish top block. It was made this way as an outcome to maximise every inch of the denim fabric.
The anti-fit does not the curve around your body; it hangs on the hips and usually worn two sizes too big. Besides, the advantage is a great comfort and more space behind the seat, which makes them accessible for skateboarders. See 501 LOT number jeans Denim Encyclopedia.