Ripley’s Believe It or Not started becoming irrelevant by the mid-1960s. The main culprit was TV which made those strange far off lands not so strange and far off. It also became easier to fact check Ripley’s.
Maybe Ripley’s Believe It or Not actually started dying when Robert LeRoy Ripley kicked the bucket back in the mid 1940s and the Kings syndicate simply found others to carry on. (Believe it or Not: People have actually been named LeRoy!). As many cartoonists will tell you, the people hired to carry on a syndicated feature never are as good as the original. The original was done out of a labor of love. After that, it’s only for pure profit.