It could have been strictly his own perverted fetish, with only Ghislane Maxwell in on it. Even so, it's still worth digging in to. At a minimum, he had "friends" visiting and traveling with him who saw nothing weird about underage girls tagging along.
Where do you think the money came from to build and run Islands, Round up girls from all over the world, Run tons of charter flights,etc...
This was a business. The elite were the clients, financiers, and the protectors of that business.