@Felthry My guess is because steering geometry typically only lets the wheels themselves move so far, and a predictable amount of angular deflection per degree of control input is seen as just a good idea?
@starkatt but some cars still have much more sensitive steering than others
our current car (a prius) turns the wheels _way_ more for a given amount of steering than our previous one (a saturn vue) (that previous one had such a wide turning radius that it was actually frequently annoying)