The eyes are far more subtle and sensitive to information, which is what differentiates "good" paintings from "bad" paintings. You could change the tiniest detail in a painting and totally change the emotions people feel about it. Paintings can access the parts of our brain that process human faces and deep memories.
Fish on rice, on the other hand, is a fairly simple combination of flavors. Most of the flavor comes from the fish. Sure, the quality of the fish matters, but I'd bet if you A/B tested "good" vs grocery-store sushi, people would randomly choose one or the other as "better". To put it another way, I don't believe in objective quality of sushi. I've had grocery store sushi that was better than super-authentic, super-expensive sushi.
This all reminds me of people thinking wine is an art and has much more subtlety than it has[1].
1. http://io9.gizmodo.com/wine-tasting-is-bullshit-heres-why-49...