Because "fewer side effects" is such a massive overgeneralization that it's meaningless. Side effects are different for each drug and there's no reason to assum

Because "fewer side effects" is such a massive overgeneralization that it's meaningless. Side effects are different for each drug and there's no reason to assume the patient would prefer the side effects of an ineffective SSRI to an effective MAOI right out of the gate. Additionally, each doctor wants you to try the less-effective drug for months at a time, each revision in the medication requires an expensive and time-consuming follow-up appointment at which point the doctor won't remember anything about you anyway, and SSRIs have their own non-trivial side effect profiles and withdrawal symptoms. It's just not as simple as -- or at least shouldn't be as simple as -- "oh, this one has fewer side effects!" It's especially bad in the case of SSRIs, because to switch from an SSRI to an MAOI or vice-versa, you have to "wash out" (that is, go unmedicated) for at least two weeks, during which time the person is unlikely to be functional regardless of their natural chemistry because they'll be withdrawing from the old medication.