Why hasn't marijuana been legalized?

Scientists have shown marijuana is less harmful than coffee and hemp can be used in so many ways. The Gateway Drug theory only exists because it is illegal and when you create a black market for something it will coincide with other ones. It does not kill brain cells, the entire experiment that 'proved' this was monkeys forced to wear gas masks only showed brain cell loss because they were deprived of oxygen, marijuana research has actually shown it can stimulate brain cells. The point is we are still listening to NIXON. One of the least liked presidents ever who is commonly ridiculed and hardly respected. His War on Drugs is still happening today. So the question is what is the problem the government as with marijuana? Is there not as much money to be made? Will it take away from the pharmaceutical industry? This prohibition has been uncalled for and only came to be because of horrible 30's propaganda saying blacks have a disease called Reefer Madness and horrible other things. Please explain