There are few Mujtahids because of the following reasons:
(a) Ejtihad is the stage of the highest Level of human ideological thinking at a given time. It is natural that starting from zero, that is, human childhood to reach to such level is a long way to go with so many obstacles on the way. Ph. D. has something common with Ejtihad in terms of thinking but Ejtihad has much more than Ph. D. as regards the quality and quantity of knowledge and thinking. This is one reason which makes Ejtihad so rare.
(b) The subject of Ejtihad is an abstract thinking which makes it difficult to get through. It is not easy to organize the ideas analyzed through the years and years of hard work and put them together, coincide and apply them to particular purposes. An accord between the analytical and synthetic process in a system requires a properly educated mind.
This is another reason why it makes it difficult for one to get through the subject of Ejtihad.
(c) The conditions demanding a certain standard of moral discipline are other factors contributing to make it more difficult. A Mujtahid is required by the system of Ejtihad to carry on this task as a social obligation which means that one has to do the work without any intention to have worldly gains thereby like to become famous, or get to the post of Leadership or have greater part in the material gains of life. A Mujtahid is required to have the best possible accuracy in his ideas and practice if he likes to be a Mujtahid, away from worldly gains which in practice is another reason to make Ejtihad difficult.
(d) Because of the western influences, religion was thought of as having nothing to do with the system of government, economy and other social activities. Isolation from the society, deprivation from the social opportunities combined with many other factors had been making it almost impossible for one to get through the subject of Ejtihad. The school of Ejtihad had no other place to flourish and it was forced to take refuge of the desert in Najaf (a city in Iraq) where there is no economical resources. There the students of Ejtihad had to continue their task and many of them would tell us that because of financial hardships time and again they could only spare their lives with the skins of watermelons after being thrown away. Because they did not want to show others their difficulties they could only get those skins at night in the dark when no one could see them collecting or washing then using them instead of food. Thanks to their patience, courage and persistence which kept the school flourishing. For these reasons it is not easy to become a Mujtahid.