So, this ad has been popping up _a lot_ in my timeline and it annoys me. The reason designers build art sites on a white cube / black box esthetic is simple: If your art website's design is memorable, it's detracting from your art. The only thing a visitor should remember about your art website is your art, everything else should just get out of the way. It's why museums hang works of paintings and photographs on white walls.
At the end of the day, which would you rather hear:
"I love the design of your website"
"I love your art"