On the other hand, why does every single piece of art have to be solely judged by how much revenue it takes in?
They don't. However, opportunity costs do need to be considered - every penny spent on a particular piece of art is away from something else, since there's only so much coin going around. Also, public should have some say about how public money is spent.
I hate to say this as someome from the US, but the serving of yogurt from Starbucks has more culture than anything the big, mainstream movie houses churn out these days.
This is, of course, complete rubbish. Mainstream movies transmit and reinforce cultural memes. You're simply already surrounded by said memes, so you don't necessarily notice.