A lot of this would be tailoring the medication to the appropriate subset of patients. Depressions are like fevers. There are many reasons and not all the appropriate treatments are the same. General physicians might not have the ability or the patience (spelled with a ce) to discern who would best benefit, so might be tempted to just toss the Medicine Of The Week at Mrs. Gloomily and tell her to come back in two months. And as the approach of Obamacare (unless halted) further curtails physician to patient relationships, this can only get worse.
It is the Holy Grail of psychopharmacology to divine the proper class of psychoactive drug for each patient ahead of time or even type of therapy drug-based or not. Lots of work across different disciplines going on toward that goal.