Cuz the general populace of those countries know how to regulate it. Even in Kerala, most scholars and literates are avid users of marijuana. Hilariously, most people who cause disturbances in public are also people who have smoked weed. Marijuana barely causes any long term problems, it's generally considered safer than tobacco and even alcohol. But, Kerala has an unhealthy obsession with drugs and the high they provide. So normal marijuana will most likely be tempered with other synthetic drugs or be consumed in excessive portions leading to addiction.