Frayed and White Marks on Outside of Fly/Zipper

The front of the fly/zipper on all my pants after enough time become unsightly. On dress style it's usually the dye wears out and there's a thick white line. On some (several Dockers pairs) it becomes frayed, even splitting the double material layer.

Why is this happening and what can I do about it?

Embarassed

Frayed and White Marks on Outside of Fly/Zipper