If they had paid enough attention in school to understand art can do more than deliver booba images, they wouldn't be fascists.

Genuinely, though, it's because fascism as a mass movement is currently in its transitory stage where it hasn't found a solid economic foothold. The American petit bourgeoisie is not anxious enough to really cause fascism to crystallize into a solid movement with a complete platform. This is useful for fascists because being vague and abstract allows them to appeal to more people who are just alienated enough to reject liberalism. Keeping everything down to just aesthetics in this ridiculously childish way is all they can do, which ends up working against them as well. I expect that if they had a more organized movement, the aesthetics would remain just as shallow and they still wouldn't understand art, but they'd be at the book burning stage so we'd have bigger problems at our hands than which side has better art.