Oberon passed it after he became ruler of his entire race. He did this, because he was disgusted of the behavior of his kind toward mortals. Maybe Titania's action which led to the divorce between her and Oberon was the catalyst for him to bring this spell into force.
Avoiding the Law
Oberon's Children can get around it, if they are clever enough. Because the key word is 'directly'.
- They can look their actions like coincidence to the mortal (as the Coyote did).
- Interpreting the law at will (as only Oberon can do).
- Arrange a situation in which everyone acts as the Fae wants (as Titania, the Weird Sisters and Puck did).
- When the mortals acted first (maybe wishing for something) and the Fae only "reacts" (as the Weird Sisters, Anansi, Puck, Raven and Grandmother did).
- Acting in the order of someone else (as the Weird Sisters and Puck did).
- Acting in a mortal form (as Titania and Banshee did).
Maybe it is enough to let the mortals think they are acting as they want.