WOW alot of interesting info here but I think some missed the mark, and most didnt even answer the question.

Q: why did centerpulls give way to sidepulls?

A: Because the tire clearances changed.

Centerpulls are a form of cantilever brake exept it is only one piece ("caliper" or whatever) the longer the reach the better they work. They have more "mechanical advantage" (what a confusing term). they just work better when they are longer.

Sidepulls work better when there is less clearance. And honestly, nowadays the clearance is so small, its hard to find a bike that you fit a freaking set of decent fenders. You have to buy some speacially desinged Mickey Moused fender-like creation to have fenders. Heck they even have those stupid "seatpost clamp-on fenders".

....OK rant over sorry.