It's not practical to design everything in the world with the very slowest people in mind. The efficiency losses would be huge. Imagine if every pedestrian crossing light went for five minutes. Vehicular traffic would grind to a standstill.
Actually, there was a study in the UK a couple of years ago that didn't get acted on, but which demonstrated that pedestrian crossing lights in British streets allowed so little time for crossing that able-bodied teenagers had to hurry -- middle-aged, elderly, unfit, or handicapped people really need about triple the time.
The solution is probably a combination of the sensor-controlled systems showing up in newer crossings in the UK (IR sensors block traffic by setting a red light until the crossing is clear) and cutting down on automobile use in densely populated areas like urban cores. Ahem. (Hint: why should your one ton rolling steel status symbol trump anybody else's right to use the highway?)