Good question. In a regular transistor, the gate does have capacitance but this is generally viewed as an inconvenient side-effect. For a capacitor, you make th

Good question. In a regular transistor, the gate does have capacitance but this is generally viewed as an inconvenient side-effect. For a capacitor, you make the gate much bigger so you get more capacitance. The other difference is that in a transistor you're connecting to both sides so you get a switch but the capacitor just connects to one side (handwaving a bit) so there's no switch action.