Because some people can't separate reality from fiction and those very people are the ones writing articles about how the Joker movie "problematic". People aren't allowed to watch a movie and have fun anymore you see, you have to send the right message. That you're absolutely as progressive as you can be. On the bright side the people who are obsessed about this movie are a vocal minority, it only seems like there's a lot of them because they occupy a lot journalist positions at various publishers, allowing their rhetoric to be a lot louder and obvious than it would be otherwise. I wouldn't worry about it, just go see the movie and support the cast that worked on it and this "controversy" will peter out.