Even if you start with the premise nobody is going to jail (which is blatantly untrue - I personally know people with possession charges), getting caught with small amounts of drugs can ruin the careers of some people, including my own career. Think people who must hold a professional licence, people who are subject to background checks (including coders who work at medium to large companies), people who work with children, people who work in certain safety critical industries, people who hold security clearances, etc. There was an FBI agent who was fired recently for testing positive for thc from using CBD oil, the federal government's position is there's no legitimate reason to test positive for thc.