Man, this is such an interesting comparison! IMO the main difference is their chosen social scenes. Cunanan’s whole thing was that he wanted to be part of the true social elite; he was interested in being around wealthy older businessmen, celebrities, famous or successful people, and was immersed in this HIGHLY status-conscious section of gay male 90s society. A lot of people in that milieu would have been very savvy and used to spotting and avoiding social climbers/scammers/hangers-on, and saw him for what he was pretty quickly. (Although it’s worth recalling that many people believed his stories and others who didn’t nonetheless put up with him, even knowing there was something weird going on with him, because he had status in their scene and appeared to have had a lot of money to throw around.)

Andy has always operated more on the fringes of society and particularly within fannish circles. He’s always tried to portray himself as the Cool Guy, but in a way that really only seems cool to people in those circles, and he could get away with his more offputting qualities because the people he was dealing with either weren’t equipped to spot them or would have accepted them as quirks (cf the Geek Social Fallacies, which I truly think explain how he got away with like 70% of what he did). He’s always made a point of surrounding himself with young people with minimal life experience, vulnerable people and people who are very tolerant of apparent weirdness. Big fish small pond.