Why do some people take Фан fiction offensively as a canon when it comes to having a fun time?

Because in Deviantart, I've written something about a crossover what if couple of Naruto, But it has to do with konoha High School related because no one can enter the ninja world. Plus, the uchiha clan never gets killed by Itachi. I also made him pair with someone else instead of Izumi, but that's only a fanon couple, not canon.