A checkmark on a calendar honestly records a fact, but it does not by itself create an incentive to come back tomorrow. The brain needs not just information but a small bit of reinforcement right now — otherwise a distant goal like "get fitter by summer" loses to the immediate urge to put off today's workout. A reward, even a virtual one, works as a small signal that "this was not for nothing."
There is a flip side too: gamification does not work as a substitute for meaning. If someone deep down does not actually want the habit itself, no amount of points will keep them going for more than a couple of weeks — at best it buys a bit more time to reach the point where the habit starts paying off on its own.
There is a third, less-discussed effect: game elements lower the barrier to entry for people who find an ordinary task list boring by itself. Some people engage better through visual progress, collections, and clear intermediate goals. That does not make them less disciplined — they simply have a different channel for holding attention over the long run.
A sensible rule of thumb is to treat gamification as an extra layer on top of honest record-keeping, not a replacement for it. A "done" mark has to stay truthful regardless of how many coins or trophies it earns — otherwise the whole reward system starts working against the habit, encouraging padding for a nicer-looking number.