Why would I plug sensors, that sip power, into a power point? When I have humidity/temperature, light, motion, etc in every single room how many freaking power

Why would I plug sensors, that sip power, into a power point? When I have humidity/temperature, light, motion, etc in every single room how many freaking power points am I meant to have in my house, aha. Maybe American houses have walls absolutely studded with power points but most other places don't.