It'd be difficult to have Meowth act like a wild animal, yet also display the intelligence of a human. Meowth isn't just a Pokémon that can speak human language, he's more intelligent that most Pokémon. If our pets were as intelligent as us, I'm sure they'd choose to sophisticate themselves by learning to use forks instead of eating off the floor and they'd bathe in a tub rather than lick themselves clean. Meowth has the intelligence to do those things, so why would he choose not to?