Look, had the biological theory had no basis in fact, medications would have been no more effective than placebo in clinical trials. Why are many medications more effective than placebo? Is there magic at work?? There must be some rational explanation.
Clearly there are many factors at play, and the biological one is a big one. The thing is, people who accept the biological cause theory also accept that the environment plays a role, but the reverse is not always true as we can see here.