There's a few possible reasons this can happen. First is that the side effect profile of one option is much better known or tolerated, so the doctor will defau

There's a few possible reasons this can happen. First is that the side effect profile of one option is much better known or tolerated, so the doctor will default to it. Second is that the doctor knows the insurance company / government plan will require attempting to treat a condition with a standard cheaper treatment before they will pay for the newer, more expensive option. There's always the third case where the doctor is overworked, lazy or prideful and doesn't consider the patient may have some input on which treatment they would like, since they didn't go to medical school and what would they know anyway?