This sort of attitude toward art is really common, and I’ve thought about a few different things that might be contributing to it.

For one, in the US at least, basically all of our education in literature prior to college is geared around standardized tests, and these tests need to have straightforward, objective answers (generally multiple choice!). So the questions end up being like, what is the author’s purpose in writing X, or what is the attitude the author has toward issue Y, or what is the contradiction been the author’s points in paragraphs G and H, etc.

I think if this is how you’re taught to think about all literature, it’s not surprising that so many people think about art as a kind of puzzle to decode with a single, objective, correct answer, and that bringing in cultural or political context is somehow cheating.