Why do all categories have a max number of 167 pages?

All product categories have a max number of 167 pages or lower. But surely the number of pages ought to to exceed 167 in some categories. If there is a max, it will have to mean that some design will not be shown if one looks at all the pages. But WHICH designs and how does this kind of sorting work?
Anybody who can explain it for me?
Best regards
Bjørn