"The point of art is to transcend politics, even when it's political, i.e. Richard III. But you'll never convince some people of this fact"
Art can have several points. One of those is to say something true about the human condition. Politics is a part of the human condition. Ergo, it is not necessary that art always and only exclude politics.
You brought up Steinbeck, and some of his works are blatantly political.
Actually, I didn't bring up Steinbeck, at least I don't believe I did.
But I still stand by what I say, at its best art transcends politics. If mentioned at all, politics is a plot element.