The founders of the organizations were blessed with the ability to organize and they laid out the designs that would attract potential members into their organizations. If one were to examine the mottos and crests of each organization, he or she would notice striking similarities between each of the crests, rather the similarities be the elements of the shields or similarities in mottos. The answer is simple.
People have different ways of achieving their goals.
Each fraternity and sorority has its own mottos, passwords and handshakes. But, just as cars are designed differently, they are all used for transportation. People are the same way. If one studies Physics or English, the goal is to receive a degree of some sort. Fraternities and sororities are the same way.