You need to learn all of the drugs because they're the ones you're actually giving, or your patient will be prescribed by other physicians, and thus you need to know their indications, side-effects, interactions, etc. That's not some esoteric, "why should we learn this" sort of thing. Furthermore, most drugs continue to be used basically forever, unless they are found to be unsafe. We discover new indications for old drugs all the time, and you'd be surprised at the utility of some medications, which can stretch across a wide range of pathologies (aspirin, valproic acid, hell, even some antibiotics like erythromycin have additional effects we're just starting to appreciate). Plus many of those new medications may not work for one patient, but an older medication will work astoundingly well- new doesn't mean better, it just means another option. If you don't like continuously learning, medicine is definitely not the field for you. I learned things in first year that are already being thrown out the window and we're unclear as to whether the latest findings or the old stuff will be present on the boards (the standards for cardiac markers, for instance, when diagnosing current and repeated MIs). We even have to learn a lot of very archaic information about obscure diseases that you will very likely never see because they demonstrate physiological or pathological principles that no other disease can. And a resurgence can always happen, or you could get a patient from an endemic area, so you never know.
We're very much in the infancy of medicine still. We didn't even have antibiotics until around 70 years ago, genetics wasn't understood in the slightest until very recently, and our surgical and medical treatments are actually often very crude (despite what television might have you think). If you want to be a doctor, you've got to embrace two things. One, you can never stop learning, or you'll be a damn terrible physician. Ignoring research and the evolution of the profession will literally kill your patients. Two, many of the things that you do will be looked back on by history as barbaric and crude, but necessary, because we're nowhere near the perfection of medicine. Almost every surgery, every procedure, and every medication we give today will likely be either eliminated or exist in a substantially different form in one hundred years, because medicine is essentially a technological field, and technology is evolving at an exponential pace.
History is fixed, aside from a finite number of facts that arise within your lifetime. History grows slowly, not evolutionarily. Medicine is evolving, alive, growing. If that isn't for you, go far, far away, because it will make you miserable.
