Yea, there ain't any such thing as a simple sensor that can correct drive the wipers. Even the ones in use on other vehicles probably require a lot of code to make them work.
Look at Tesla from the longer viewpoint. The goal is not to make the wipers work for you, the goal is to make the wipers work for the Autopilot. And what's the best way to do that? Exactly like you do today, look out the window and see if your visibility is hampered. That's a lot easier said than done. And before you return with its obvious for a human, that's very afar from the truth, as I go a lot longer without wipers than my wife does. In fact, for me, some rain situations, for me, are better with the wipers off, than on.
And from a slightly different viewpoint, it is imperative that an Autopilot know when it's vision is reliable or not. So no matter what you want, that algorithm has to be created, just to know if safe automatic driving is possible.