A lot of the simplification and rationalization that was the initial selling point for the tax bill somehow got traded in for large tax decreases for the wealthiest before it was signed. In my generous moments I think that they really did intend simplification and were simply bowled over by the other interests.
In my less generous moments I notice that they keep saying that they are doing A, and instead do B. Again and again.
The new tax law that was passed I thought might eliminate that loophole, but the proposal was nixed in the final bill.