I agree but there are only really two options;
1) take a hard line - players have to choose where their loyalties lie and aren't considered for test cricket. The downside of this is you risk losing the likes of Stokes, Buttler to the test match game altogether and water down the product.
2) Have a rotation policy where on occasion these players miss some test matches which also weakens test match cricket by perhaps to a lesser degree.
You are more confident than I am. I'm sure he prefers test match cricket but in a sport where he has only a few years left he will want to maximise his income I would have thought.