some lights keep their microprocessor on, just to monitor the switch

better designs will ‘sleep’ the micro in a lower power mode, and pressing the button will cause it to wake up and start running the light, using more computing power

as far as specific lights, you would have to know about the design to really know where the drain might be, and the reason

older controllers may not have supported ‘sleep mode’, or the programmer didn;t bother to use it, or it could just be a circuit error, or as you said, any LEDs that stay on like in the button

wle