1) Nobody likes to admit they were wrong... Governments least of all.
2) It's all about power and control. Legalize weed, and the powers-that-be give away their most useful tool in exercising total control over the general populace. By criminalizing an otherwise harmless act, the Government by its decree instantly makes millions of Americans "criminals." Now that's power. That's control.
3) What in the world would they do with all that free court time and prison space?
4) Where would they find another so convenient an excuse to turn thousands of rapists, muggers, murderers and pedophiles loose on the public if not the overcrowding of our prisons created by this amoral set of Drug Laws?
Power, control, and the refusal to admit their error.
The Jackboots suck huge mung.
;-\
5) MONEY. The war on drugs enriches politicians, lawyers, bankers, drug lords, the drug rehabilitation industry, suppliers of goods and services for law enforcement, and private prison corporations. It provides high salaries and great benefits for DEA agents and law enforcement officers, judges, prosecutors, prison guards, probation officers, etc., etc.
6) EMMANUEL GOLDSTEIN. The war on drugs creates enemies upon which the people can direct their hate. Not only does this distract the public from government malfeasance, it is source of a large fraction of Hollywood scripts that make a lot of money and reinforce the perceived need for the war on drugs. Most importantly, it creates the impression that government is actually doing something constructive to address the real and tragic problem of drug abuse.
7) ASSET FORFEITURE - The war on drugs has created a huge revenue stream that bolsters state and federal coffers as well as funding military hardware and other toys for local law enforcement.
8) EASE OF PROSECUTION - It is hard work to prove guilt in real criminal cases. But every drug possession is an easy case to prove since the crime is defined by the evidence. This greatly simplifies the work of prosecutors and boosts their conviction rates.
Certainly you don’t want to deprive our public servants, and those who serve them, from these benefits.
There are other benefits, of course, such as affording sociopaths the opportunity to kill pet dogs at will. But these are too numerous and specific to be included in a short list.