I've read most of the posts here, and countless other posts, and everyone seems to be ignoring the most relevant point - WADA (WORLD Anti-Doping Agency) has listed marijuana as a banned substance. It's not about local, state, or even federal laws in the United States. It's not about someone's emotional trauma. It's about WADA enforcing it's regulations.
It does not matter whether marijuana use is legal in Oregon, or if Richardson found out about the loss of her biological mom. It's not about how you personally feel about marijuana use. It's not about some racial inequity that marijuana was outlawed in the US because of racism, and those laws were instituted because white people wanted to target black people.
It is about the fact that throughout much of the world, it is illegal. Do some research. Sure, in some European countries it is completely legal, in others for medicinal purposes, and in others just decriminalized. But the fact remains that many member nations of the IOC and under jurisdiction of WADA have not legalized marijuana, and don't intend on it. Therefore it creates a level playing field. Until a majority of nations attitudes change on marijuana, it doesn't matter what you might think here in the US.
As long as marijuana is illegal in a majority of countries involved in IOC, WADA, etc, then it will probably remain on the banned substance list. If you're subject to drug testing and WADA regulations, then you know this. If you violate this and get caught, you get suspended. Until the rule is changed, you play by the rules. Once we start to ignore the rules, for whatever reasons, drug testing and enforcement will become even more of a joke than it already is.