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All games have loops within loops within loops! :)

The best games have a layering of loops of different frequencies, which complement each other. That's what gives games that "one more turn" feeling, if at every turn you're confronted with multiple decision points with different result horizons. So at every point in time, some decisions ripen and are ready to collect, while others require attention but will have payoffs at very different times in the future.

Edit: for roguelites like STS I would count a single run as the core loop. Especially in the presence of metagame, the benefits gathered during any single run add up, and make the player that much more interested in coming back and giving it another try.