What is the reason for the 4 Math-habs?

Answer

The reason for the four Math-habs is Allah's Will and Wisdom. Since Allah Ta'ala willed that the acts of the Shariah be followed in different ways, we find Rasulullah (sallallahu alayhi wasallam) acquitting himself in different ways in the same acts. If Allah Ta'ala had not desired these differences, He would have ordered His Nabi to discharge all acts of the Deen with uniformity. Furthermore, there are not only four Math-habs. There are numerous Math-habs. However, the Four Math-habs constitute the Ahlus Sunnah Wal Jama'ah while all other ways are deviant and crooked.