Overeating is the "cause" of obesity because that is the mechanism of action that facilitates obesity. How else could one reasonably become obese?

Overeating is the "how" not the "why" -- at least, that's how I see it.

It would be like saying alcohol is the root cause of alcoholism, when in reality, the root cause of alcoholism is often much more nuanced. Hence why many people with addictions tend to be polysubstance users or "hot swap" to a new vice after abstaining from another. It's not about the mechanism of escape, but rather the need to escape.