Speaking like a clueless idiot, how come so many speakers used foam or fiber surrounds? Wouldn't rubber or some sort of synthetic material be better and last longer?

The simple, and easy answer, is foam is cheaper. Rubber or fabric impregnated surounds cost more due to the process to manufacture. Though nowadays it's somewhat close betwen the three, most manufacturers expect that people will replace the speakers in question within a given number of years so the necessity for them to last a lifetime is not a concern.

Plus with advances in the science of foam products you can now get a surround made of foam that will probably outlast you unless it's subjected to extreme conditions such as dust and heat.