Not that simple. Watching a couple of docs on pot will help you better understand why decriminalization/legalization hasn't happened. I specifically recommend The Union: the business behind getting high.
Quick breakdown:
Let's look at some of the entities making money with pot being illegal.
lawyers who represent offenders, private prisons, prison workers, police officers enforcing drug laws, govt revenue from citations and tickets, judges, drug testing facilities, etc.
legalization would mean decreasing the workforce in all of these areas. More job cuts, more layoffs, less future employment opportunities etc
I imagine the real reason to enforce the status quo boils down to hard economics. I posit that more money is made in the current illegal status than it would if legal. OR the potential increase in revenue would be too minimal to justify the other "societal risks" involved...
This should get you started on expanding your myopic view on the impact of decriminalization/legalization (which i once shared).