Not to buy it? Lucian is currently bugged. One of his abilities, the one people will typically want to start with, can randomly cost double mana for no added benefit. If this bug happens a lot early game, you run out of mana much faster than you should, and you can't fight to save yourself if things go wrong. A friend of mine who played him on the PBE described him as "clunky" compared to how he was on the PBE. Having seen him play as other ADCs, and play as lucian, I believe him. Lucian's skin isn't nearly as neat as so many other skins you COULD get. 3 reasons, there you go.
The guy who thinks Karma is a viable champion. Hero's aren't made. They're cornered.