Someone didn't watch the Lucario movie.
No, I did not. Lucario doesn't look Psychic any more than he does Steel, was my point. Furthermore, the abilities of a Pokémon in a Movie or in the Anime is hardly something to change anything in the entire franchise. (Pikachu vs. Onix and Aiming for the Horn, for example.)
If he was Fighting/Psychic there'd probably be just as many people wondering about his typing as there are now. In fact there's a large pool of Pokémon whose typing is something to wonder about, either in moves learned or by the looks.