A kilowatt hour is 3.6 megajoules. It's used for the same reason lightyears are used to measure distances in space, it's easier to say Alpha Centauri is 4.396 light years away than 4.159x10^16 metres.

[–] merc@sh.itjust.works 1 points 3 hours ago* (last edited 2 hours ago)

Astronomy uses special units because the SI units are more than 10 orders of magnitude different. You'd have to use really exotic prefixes like "zetta" or "yotta" if you wanted to keep using metres.

The difference between a kilowatt and a megajoule is just 3 orders of magnitude. You just have to switch from "k" to "M". People are already familiar not only with "M" but with "G" and "T" because of Megabytes, Gigabytes, Terabytes, etc. There's nothing about kilowatt hours that's more intuitive or easy to use.