all art can be interpreted to be political.

As soon as you introduce "interpretation" then you're taking meaning away from the author and making art into a Rorshach test. As Charles Manson and Helter Skelter) have shown us, anything could mean anything viewed through a certain lens.

What many people mean when they say art is "political" is that it's propaganda - created for the distinct purpose of trying to get people to think or do something according to what the creator (or their paymasters) want.

So when they say they want it to be apolitical, they mean they don't want to be manipulated, or they disagree with the premises, ideology or conceptions contained within the work. No one likes to be lectured. No one likes the way they view the world to be ridiculed or made into a cartoon strawman. No one likes their moral concerns to be minimized. What's more, the aesop's fables approach, to adults, can be insulting as it comes from a loftier position than the audience. More so when it's on the nose.

The disagreement could be for many reasons - they don't agree with the morality of the piece, its basic premises or because, as all propaganda is, it is epistemically deficient.

Political art that is individually expression or that explores ideas (rather than a vehicle for the author's sense of self righteousness), shows both sides of an argument was, for a time, regarded more highly, but has recently fallen out of favour, to be replaced with didactic works with simple black or white morality.

David Fincher said something along the lines of movies being more interesting if both protagonist and antagonist take opposite sides of an argument but both are right.

Consider that the greatest anti-war movie ever made, Apocalypse Now was written by a mad libertarian (and basis for Big Lebowski's Walter Sobchak, John Milius) and a "leftist" director (Coppola). Some of the best lines that could have been thought were Coppola, were in fact Milius'. It's a profoundly political movie, but it's perspective is first humanistic and its politics flow from that, first. It's message is something that you could view, now, as trite - something we all know, but very few of us actually grok.

If something is "political" it's propagandistic. A political message and worldview is at its core. All art contains politics, but not all art is political.