They use marijuana and then immediately get depersonalization. For many people, marijuana will be the thing that pushes then over the edge into an anxious, dissociative, or psychotic episode. This has been empirically proven. Everyone's reaction to marijuana is different. Some people feel happy and more at peace. Some people get a clearer understanding of what their emotions are and what they want to do.
As for, "Why let anything get in the way of your life," marijuana isn't my life because every time I use between 10mg and 20mg of edible for instance I have an anxiety-depersonalization attack. This dosage is in reference to THC cannabis. I think Delta-8 derives from hemp and is less strong.
As for marijuana as a treatment for depersonalization, I wouldn't pull something like that out of my ass, especially not when marijuana can cause depersonalization. If people want to use a drug then just use it without nonsense reasoning.