Why isn’t Botox a first line treatment as a preventative?

After physio, water, Tylenol, etc, all the basic things, why isn’t Botox considered the first treatment? People go on topirmate or other brain meds. Botox does not enter the brain and has seemingly few side effects along with very good results. Seems the only major downside is the cost.

I’m pushing hard to get Botox covered by my insurance. I don’t want to mess with many brain meds before I do this one.