ML performs very well for specific well defined tasks that have an obvious outcome and are highly narrow in scope.
Cancer is a disease that we can't even treat ourselves in many cases. It requires a great deal of creativity and critical thinking to reach solutions on a case by case basis. Who is so arrogant they thought this should be replaced by a bunch of overhyped software?
Maybe it's counterintuitive, but it makes a lot more sense to use ML for cancer than say a broken arm. There are so many systems interacting in cancer that affect its progression that humans really are at there limits in trying to understand them.
And as others have said, no one is letting Baymax loose in the oncology ward and firing all the doctors. This is just one more tool in a doc's tool belt -- and far from the only that will give misleading results.
Bacterial infections also have a ridiculous amount of systems involved and yet that was figured out by humans.
I don't see how ML helps with cancer at all right now. The problem isn't the amount of data. It's the quality of it.