Yeah! i mean the stats show they are like us in terms of the habit/addiction. Monkeys are clever animals, as are rats.
Maybe its some kinda disturbance reaction... like the one in the Rat Park article you gave (thanks). Meaning they are not native to that part of the world, just like rats are further from metal cages than they are the 'Rat Park'.
Hmmm... maybe some kind of evolutionary detachment causes the 'stress' for the monkeys?
Hmmm... but how is it for 'humans'?
$60.000 question i guess...