Who currently controls the domain? One of the ways stuff can be lost is if a new domain owner fiddles with robots.txt. (The Archive has recently changed their policy about that)

We have also seen an upsurge of the use of robots.txt files to remove entire domains from search engines when they transition from a live web site into a parked domain, which has historically also removed the entire domain from view in the Wayback Machine.

https://blog.archive.org/2017/04/17/robots-txt-meant-for-sea...