actually they have started. they won't ever get too extreme because their wheel wells won't allow it, but they're surely trying.

 

245-40 on a 10" wheel.

And that is all dependent on suspension design. Some cars require more than others. Like my car for instance, its generally accepted that -2.5* camber in the front is proper for most amount of grip. Most hondas and other FWD cars dont need more than -1.5* to -2*