Why arw AF Points Bunched Up in the Center?

Why are AF points bunched together in the central 25% of the viewfinder? If they all have to be bunched together in the middle, what's the difference between having a 10 versus 100 if they are covering the same area?

I would really like to have five AF points (one at the center and four at the 1/3 intersection points), but I wouldn't value having a million that cover the center only.

Because of optical reasons. They don't work well too far from the center. That's also why cameras with larger sensors have their points covering a smaller percentage of the image, since the sensors are just as far from the center, but the field of view extends further.

The advantage of having more points is that it allows the camera to track moving subjects better. It also allows you to avoid re-composing after focusing a bit more, since the likelihood that a point covers your target increases.

^ +1
It's due to physical limitations. If you're curious you can look up how the AF sensors work.