Because most folks don't use more than a port at a time. Stroll through a university campus and you'll notice that most folks with a Macbook pro/air aren't using even 1 port (the charger) as the battery life has gotten good enough such that you can charge in your dorm and then be good for mixed use throughout the day.

I remember how much pushback there was about getting rid of the CD drive too, but the truth was they weren't being used that much anymore anyway.