Maybe because Bipolar is just a concept and not a medically proven illness. The same goes for meds and the way they work. And they are harmful to your body in one way or another, that's why you need to answer yourself a question whether the side effects are worth it. Depends on how you act without meds (and I don't mean after not taking them for a short period of time bc then comes withdrawal, but from a much longer point of view. When coming off meds, the symptoms often seem worse than they really are, the depression feels harder to overcome etc).

Before taking an antipsychotic, I would first go for the medical tests: B12 level, thyroid function, head scan, iron levels, magnesium, liver and kidney function, check cortisol levels to see if there's any possibility that the symptoms come from another source.

I grew very vigilant with psychiatry and the topic of bipolar since they started diagnosing it on a huge scale among young children and drug them with neuroleptics so they will be bond to these meds for a lifetime, suffering from metabolic disorders, diabetes and other side effects.