It is not weak willpower; it is designed that way. Where the hours actually leak.
Many games combine a once-a-day reward, time-limited tasks, and seasons that close every few weeks. Because skipping feels like a loss, you log in even on days you do not particularly want to. This is less a matter of personal discipline than a structure built to produce that result.
The better the game, the more reliably the next goal is already visible the moment you finish one. The experience bar is nearly full, you are one key short of a chest, a few matches from the next tier. A natural stopping point never arrives, so the stopping rule has to come from outside the game.
Perceived time and actual time differ sharply. Most devices and platforms report actual playtime, so checking a week gives you something concrete to judge by. Knowing how much you currently spend comes before deciding to cut down.
Playing a bit and then stopping rarely works. Deciding the end condition before starting holds up far better. Framing it as matches or a goal rather than minutes also reduces the irritation of being cut off mid-game.
Gaming itself is rarely the issue; crowding other things out is. Continually shortening sleep, repeatedly putting off what needs doing, feeling anxious or irritable when unable to play, and repeatedly failing attempts to cut back are the markers. If that persists for months, talking to someone is faster than trying to manage it alone.
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