The addictive nature of marijuana is just different from something like, say, opiates. There is absolutely a physical component to both withdrawal syndromes. A lot more physically visible symptoms manifest when someone's kicking heroin, but someone kicking weed might be going through some shit. A common one is: they can't sleep anymore. And now after they're pot-free, they start having dreams and remembering them again. This seems to be pretty jarring to people, if you haven't dreamed in a long time, every time you sleep, you're just in total oblivion, suddenly you're thrust back into the bizarre mindfuck of dreaming- I can see why that'd be uncomfortable. Personally, I believe that pot addiction is more about the mind than the body. Heroin addiction is more about the body than the mind. Kicking heroin can be really fast, and the worst withdrawal symptoms gone in a week- someone breaking all the habits surrounding their pot use over the course of months is probably exhausting. Probably also easier to talk yourself into relapsing- "It's just a little joint, it's not like I'm a smackhead or something." Sucks that drugs always have drawbacks, but such is the nature of the universe. Get fucked up, you might end up fucked up, it really makes sense when you think of it like that.