I can't speak to most countries, but the United States did so largely due to concerted efforts to tar it as a drug of "negroes" and "Mexicans" and to attach to it mostly-untrue stories. "Reefer Madness" is an awful movie, but it's an awful movie that exists to push a policy position.

Understood. Here's a little overview of what happened in India: https://www.quora.com/When-and-why-was-marijuana-made-illega...