You can look at several types in that list that don't have wall power easily or always available. Door and window sensors, which could be solved similar to older alarm systems, but have a significantly lower barrier to entry being wireless. There are convenience and accessibility benefits to allowing wireless battery-powered switches to control your devices. Wi-Fi can be an answer for a lot of these but there are battery life and coverage benefits to the mesh behavior of these networks without needing to spend a lot to expand your Wi-Fi coverage.

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.

> They're all plugged into wall power all the time

Most of the remotes switches, sensors, and some others are all battery powered and last at least a year without needing to be changed.

In fact, they would be largely useless or cumbersome if they needed a wire.