But people are addicts, and people can become addicted to many things not considered "addictive". Like overeating. Like sex. Like gambling.
If weed is not "addictive", why does marijuana-anonymous.org exist?
I have a friend who cannot stop smoking weed because she has had significant emotional trauma in her life. She continues to smoke despite impacts on her job and family life. Even she admits she is addicted to weed and cannot stop on her own.
Just because weed is, as you say, "not addictive" doesn't mean people can't get addicted to it.
You may be using the term "addictive" when a better term is "toxic". Alcohol, heroin, even nicotine are toxic and can cause death if enough is ingested. But when taken in smaller doses over time, the body adjusts it's chemistry to accommodate the toxins. When you abruptly stop ingesting the toxin, the body cannot handle the change in chemistry quickly enough and people become sick and can die. That's why addicts need to "detox" if they are using large quantities of toxic substances over an extended period of time.
Weed may not be toxic to the point where users require detox (or as you say - it's not addictive), but people do indeed become addicted to weed.