An Outline of the History of Restriction on Ijtihad
1. With the passage of time and betrayal of trusts, it was no longer permissible to rely upon the views of the evil `ulama, unjust judges, and the muftis who issued fatwas for profane ends (ahwa').
I say: But there is no obstacle to relying upon those `ulama', besides the four imams, who do not possess the above-mentioned characteristics, because the allegation that all others were evil except the four imams is something which no Muslim would have the temerity to claim.
2. When the other madhahib gradually became extinct, the majority of Muslims inclined towards these four madhahib, and the Prophet, may peace and God's benedictions be upon him and his Household, has said (`Follow the majority').
I say: How could the Prophet, may peace and God's benedictions be upon him and his Household, have said such a thing, and how is it conceivable that he would make it obligatory to follow those who are considered sinful by the Book of Allah, which declares:
Surely most men are transgressors. (5:49)
And you will not find most of them thankful. (7:17)
There are a large number of such statements in the Qur'an and hadith.
Moreover, the better recognized version of this tradition is ,  wherein there is a command to go to big cities because they are centers of various kinds of learning and have other benefits lacked by villages.