To understand why amateur and professional cryptanalysts alike have not given up on the Beale ciphers after hundreds of years, the reader must refer back to a quotation in the beginning of The Code Book. Singh so appropriately referenced John Chadwick in saying, "The urge to discover secrets is deeply ingrained in human nature."
I believe the intrigue behind the Beale Ciphers is not as much motivated by the promise of literal tons of gold, but by the natural desire to discover the unknown. The prospect of an unbreakable code, that has duped some of the brightest minds of the past century, not only challenges, but insults those who feel the inclination towards discovery. It is the push for a higher understanding and a greater knowledge.
I experienced similar feelings at young age. As I was riding the subway in New York City on vacation with my family many years ago, I realized I could not understand anything being said around me. The car was packed with people of different ethnicities and backgrounds and the melting pot of tongues fascinated, as well as frustrated me. I had a desire to listen and understand. While none of what was being said around me were actual secrets, they were to my english only vocabulary.
I believe the reason I choose to study languages in school, is the same driving force behind cryptanalysts pursuit of the elusive Beale Ciphers. To some ignorance is bliss, but to most of us it is a constant nagging of what we lack in understanding.