The main reasons that hemp was legislated against were pretty much all related to the fact that it could almost single handedly disrupt numerous embedded ecosystems... and it is practically a weed. Just throw some seeds down in front of city hall and watch them grow.

As your image notes, hemp can be used for many, many things.

Clothing that lasts a very long time? That hurts someone...

Walls and floors that need nothing more than some mud, sand, and straw or hemp? That hurts someone...

Pain relief without horrible side effects and addiction? That hurts someone...

Fuel that doesn't require military bases all over the world? That hurts someone...

Follow the money... and things start to make sense.