Why do you say it's not? Behaviorism: That seems reasonable to me at a surface level, that one's environment and one's genetics dictate behavior... If anything it doesn't really say much in particular that's falsifiable...Ever since Pavlov and Watson, psychology has been trying to prove behaviorism is a thing (it's not).
It assumes that the behavior of a human or animal is a consequence of that individual's history, including especially reinforcement and punishment, together with the individual's current motivational state and controlling stimuli. Thus, although behaviorists generally accept the important role of inheritance in determining behavior, they focus primarily on environmental factors.
I'm not sure if I see your point... Define direct and causal? I question your assertion because I lack a general context for psychology, if we're going off of purely physical laws: some set of probabilistic rules dictated that viewing your message set off a chain of neurons firing that made me write a message in response. But maybe that's not what you're getting at...