There is a fatal flaw in the practice of trying to understand the "causes" of human behavior in the same way that we understand the causes of an apple falling from a tree or some other purely physical phenomenon. The flaw is that people are equated with unconscious things when analyzed this way. Clearly there's an important difference between people and unconscious things: consciousness. That is, people have something non-physical that guides their behavior; they have thoughts, ideas, beliefs, goals, intentions. Put most simply people have reasons in their mind for behaving the way they do. Unconscious objects have no such ability. This distinction between people and things is crucially important. The movement of things is caused by other things acting upon them, while the behavior of people is chosen by themselves for various reasons.
There are many more proposed "causes of addiction," and the fact is that none of them truly hold water because when the claim is that one thing causes another, this should be readily observable and verifiable in every case, yet it never is with respect to substance use. Causal relationships are not subjective by nature. If I told you putting a lit match to an open tank of gasoline "causes" a fiery explosion, you could test this claim. Assuming you survived the explosion, you could do it a hundred times and it will always result in an explosion. But if I told you that poverty causes addiction and you went to a poor neighborhood to survey 100 people, you might find somewhere between 5 and 20 people who currently fit the diagnosis of addiction. Why weren't the other 80 people caused to use substances heavily? Then you could go to a high priced treatment center and find nothing but people who grew up in wealth and luxury. What caused them to become addicted if not poverty? Or say I told you trauma causes addiction. If you rounded up 100 people with high trauma scores only 15 of them might also have "alcoholism." This is what the research shows. Yet people proudly claim that trauma causes addiction as if the only response to traumatic events is to dive headlong into heavy substance use. In fact, this response to trauma is the exception, not the rule - the other 85 are not addicted. Are they superheroes with magical powers somehow able to flout the law that trauma causes addiction?
These claims of "causes" are based on nothing more than probabilities and correlations. Some reliable percentage of people with depression or anxiety problems also has substance use problems (20%). This correlation doesn't indicate that depression and anxiety cause addiction, or even that these phenomena are related in any meaningful way. If there is a relationship, it could be that some depressed people think that getting high is a good way to deal with their depression, or they may even think it relieves the depression. Or it could be that heavy substance use leads to depression. There could be any number of reasons that some people with depression also use substances heavily, but there is nothing that shows heavy substance use is a necessary result of depression in the same way that an explosion is the necessary result of putting a lit match to gasoline.