Think of it this way. Defense is typically reactionary, meaning you aren't necessarily making a read, you are just doing your job. On offense, the player has to be able to read the defense and adjust accordingly.
Yes, it can be said both ways with that argument, but defense comes down to the effort you put into it. Offense requires quicker IQ thinking BEFORE you react and the skill to execute it.
Both need high IQ to do well, but offense isn't just effort. I don't care if a kid can run like Usian Bolt, if he can't kiss it softly off the glass to make the layup his effort isn't rewarded. But if all if all I have to do is teach him to use that Usain Bolt speed to get in front of the guy with the ball on a fast break, then defense will be much easier to teach.
Edit:
To clarify my point that defense is more reactionary was probably poorly worded. What I mean is, if I tell a 7ft kid with no experience to stand in front of the goal with his arms up, that is his job. Nothing else matters except what pertains to that job. If someone is trying to root him out of position, he knows it's his job to maintain it. That's all. He's not been given too much to handle even with a low IQ. Over time I add jobs like help defense, rebounding, etc. But that's just with what he can take. You teach him what he can handle nothing more and with his size and athletic ability he can be passable.
Put that same 7ft kid with no experience on offense and he has far more to worry about. Can he develop soft hands to catch an post pass, can he pass out of a double team, can he not turn it over, does he have any post moves, can he set screens, can crash the glass without going over the back, etc etc etc. Offense requires more skill than JUST athleticism. Defense you can become passable with simple rules and athleticism and still bring value to the team defensive strategy. Offense, even with the probably tip dunks and maybe some unreliable short jumpers at the end of shot clocks, you don't really bring team value on that end of the court without skill.
