Equivalently, it's the only form of fiction which some people think isn't "real". Try this on for size: "You know movies aren't real, right?" Can you seriously imagine anyone saying that? It would be utterly absurd. Yet in discussions of wrestling, it's par for the course.
A fun way to make sure you aren't invited back to parties is to convince those people that you genuinely believe the UFC is a work while pro-wrestling is a legitimate competition.
The adult fans might know it's fiction; children are still figuring out where that line sits.
Arguably the largest part of this illusion "kayfabe" has been dead for years and years - everyone knows wins and losses are predetermined. That doesn't stop promotions from using wrestling news and social media to blur the lines of what's real and fake when it comes to contracts, injuries, and alliances.