Because most people haven’t actually read Alan Moore’s Rorschach, they’ve seen Zac Snyder’s Rorschach. These are not the same character
If I remember correctly, there was talk about how closely the movie followed the graphic novel when it was being made and im sure that didnt help people want to to check out the source material.
I think most people aren’t interested in both mediums. Especially at the time most people only really experience fiction from some sort of film/television
The movie was very much an abridged version of the novels. Meaning all the nuances and hints that were disseminated throughout the pages or in the backgrounds had to be set aside until we are left with the movie version. A very “Loyal Stupid Paladin” character, which really isn’t a misrepresentation; it is the same character. Just, you are not given quite enough in the movie to see where he’s actually coming from.