I know Chatot because of Chatter, and Wobbufet because of his moveset+ability, but why Luvdisc?
Chatot is not allowed in Wi fi because people could say rude or offensive words through Chatter. Sky-drop is banned because of a certain glitch that occurs in double/triple battles. Hacked Pokemon are banned as well. In PO the reason for Luvdisc (as stated by others in comments) is only banned when paired with Politoed/Kyogre because Drizzle+Swift swim is banned (something that I still disagree with).