Reach up, pull the chain, and the light comes on. The pull-chain fixture puts the switch where the light is, and that small design choice tells you something about the houses these fixtures were made for and why they still make sense in some rooms.
The logic is about wiring, or the lack of it. Running a wall switch means running wire to it, which means planning, expense, and cutting into walls. A pull-chain fixture skips all that. The switch is built into the socket, so the fixture controls itself, and you can put light in a space that was never wired for a wall switch: a closet, a basement, an attic, a back porch, a utility room. For a lot of the housing stock, that was the practical way to add a light where you needed one.
The mechanism is about as simple as electrical control gets, which is why it lasts. A pull-chain socket has few moving parts, and when the chain or the switch finally wears out, the socket is a straightforward replacement. That plainness has become a look, too. A simple pull-chain fixture, restored, looks unpretentious and period-correct, and it suits the same spaces now that it did then, plus a few rooms where people want that stripped-down character on purpose. Put one in a closet or a basement and you have light and control in a single fixture, with no switch wiring to run.