These "chemical imbalance" narratives tend to do more harm than good by giving patients an idea that their symptoms are purely external to their own choices, and therefore completely out of their own control. Unfortunately, it's very difficult to convince suffering patients that they have some control over their situation without also implying personal blame for their problems, which doesn't go over well. The idea that the problem is faultless ("It's not you, it's just your brain!") and that the solutions are effortless ("This pill will fix your chemical imbalance") is just too tempting. The alternatives ("Read this book on study habits, leave your phone in another room while studying, use timeboxing...") are an unappealing alternative.
Don't get me wrong: Medications can and absolutely do help people, but this idea that the problem can only be treated via medication is demonstrably false. The most successful patients use a combination of medications, therapy, and healthy habit-forming. The least successful patients tend to give up on everything except the medication, reaching for ever-increasing doses or trying to play games of on-days/off-days or saving up extra medication. That's a losing battle.