Final answer:
The case remains of high interest because amateur detectives are still actively trying to solve it, which shows the case's enduring appeal and mystery.
Step-by-step explanation:
The detail in the excerpt from "A Byte Out of History" that supports the central idea that the case is still interesting to many is that amateur detectives continue to investigate the case. This detail shows that despite the passing of time and the many dead ends encountered by professional investigators, the intrigue surrounding the case has not waned. It highlights the persistent fascination and determination of those outside of law enforcement who are committed to solving the mystery.
Other details provided such as the FBI following many leads, potential suspects being investigated, and the existence of a DNA sample from Cooper's tie, reinforce the ongoing interest and efforts to close this cold case, but the involvement of amateurs directly corresponds to the public's undiminished curiosity and the case's status as a captivating enigma.