The same reason I drive a Jetta could be the same reason someone should not drive an SUV. If you can't handle it, or know where every part of your car is in relation to other drivers, peds and cyclists, then simply, you shouldn't be allowed to drive it. The gent next door to my GFs drives a large truck and well he should, since he's a really experienced semi-driver.

When you're driving a larger vehicle, you should drive proportionally slower because you might not have the experience to get yourself out of a jam that you would in a smaller vehicle. The other reason for SUVs to be required to drive at a slower speed is the sheer force delivered to lighter vehicles that have no protection against a high overhanging bumper.

Today I came within several feet of getting sandwiched between a bus cutting me off and the barrier on the way to the Lincoln Tunnel. I slammed on the brakes and was able to miss this swerving bus. He just drove on ahead. I think that there is sometimes a non-caring attitude with drivers of larger vehicles, knowing that they can inflict a great deal of damage.