Why are there four schools of thought, fiqh or Islamic Jurisprudence?

Fatwa, posted 4.22.2010, from Egypt
Religious Authority: 
Muhammad Ghazali II
Fatwa Question or Essay Title: 
Why are there four schools of thought, fiqh or Islamic Jurisprudence?

The ulama (Islamic scholars) recognised as their starting point that their conflicts were conflicts of interpretation, and do not reflect inconsistencies in the Lawgiver's message as conveyed by the Prophet (pbuh) [peace be upon him]. While it is necessary for the Muslims to follow a recognized madhhab (school of Islamic jurisprudence) in order to avert the lethal danger of misinterpreting the sources, he must never fall into the trap of considering his own school categorically superior to the others. With a few insignificant exceptions, the great scholars of Sunni Islam have followed the ethos outlined by Imam al-Ghazali. The attitude of toleration and good opinion has existed between [among] the schools.