ritalin was once heavily marketed (to doctors, not the public) for depression, as a milder alternative to amphetamines. even now, amphetamines and the ritalin preparations are often used in people with mood disorders and other problems, usually with other drugs on board.
so...i dont really know what to tell you, lol. no psych drugs 'fix' anything, obviously. the idea is to alter brain chemistry to improve someone's life, hopefully without running into terrible adverse effects and/or drug addiction, dosage escalation, etc.
if anhedonia and such are ongoing problems, then it stands to reason that something stimulating--ritalin, an amphetamine, even a stimulating antidepressant--might brighten one's outlook, at least for a while. the question for each individual is obviously do any risks or obvious adverse effects outweigh benefits? are there benefits? etc.