There has to be a rule to NOT going to planets that are stated as remote and secret in the movies. Proper or not, Ahsoka was phoned in in every Onderon scene. Again, after Gathering, the arc became about Ahsoka... Onderon was not about Anakin, Onderon was marketed as an Ahsoka arc. Obi-Wan has just one arc in S5 that focuses on him. The S2 cover was rather random if you ask me. Maybe they did not know what to do with the cover then.