In The Code Book, by Simon Singh, the discovery of cryptanalysis is discussed. It is explained that without a strong background in core disciplines, cryptanalysis is impossible to achieve. Mathematics, statistics, and linguistics are vital in the development of many methods, such as frequency analysis. Earlier civilizations lacked a certain amount of efficiency in these fields, and that is why cryptanalysis was not discovered until around A.D. 750. The discovery was made in the Islamic civilization during a time when the arts and sciences began to explode with breakthroughs. It took years to become masters of cryptoanalysis, like they were.
It is not uncommon in modern society that an amateur cryptanalyst is able to crack a simple substitution cipher using the same method of frequency analysis, without ever being formally taught it. Are all modern cryptanalysts just naturally born geniuses in the art of code breaking? No, that's not likely. Instead, our society has just developed significantly since the year A.D. 750. People are given a better foundation when growing up in the arts and sciences. Mathematics, statistics, and linguistics are taught to all people, in varying degrees of course, but these fields are still emphasized. Civilization has advanced so far that many people have a basic understanding of subjects, that very few people knew about in ancient times. This is the main reason why amateur cryptanalysts can decipher substitution ciphers with out extensive training. To people in today's day and age it is just a "logical" way to attack enciphered messages, opposed to the people in ancient times who worked tirelessly to unlock the secrets of mathematics.