If a person hadn't experienced a debilitating depression it's hard to imagine what another person is experiencing. All those walks in the park and hobbies sound logical and wonderful, on paper. Reality is a bit different.
Modern medicine is irreplacable but relying solely on medication is a pitfall of modern treatment. It turns out, for example, that chronic pain and depression are interlinked. A messed up neurochemical balance contributes to the erroneous interpretation of signals by the brain as pain (even when no bodily damage exists anymore). So what I'm saying is that while it may seem pointless initially to do that which falls flat in the estimation of a depressed mind (say due to anhedonia) those brief but regular walks in the park contribute to re-stabilization of neurotransmitters along with the medication.