I believe it's just a matter of intuitively useful units. There's simply too many seconds in a day for people to have an immediate grasp on the quantity. If you're using a space heater or thinking about how much power your fridge uses kilowatt hours is an easy unit to intuit. If you know you have a battery backup with 5 kilowatt hours of capacity and your fridge averages 500 watts then you've got 10 hours. If you convert it all to watt seconds the mental math is harder. And realistically in day to day life most of what we're measuring for sake of our power bill, etc. is stuff that's operating on a timetable of hours or days.
True. Otherwise we would be using square meters for measuring gas mileage instead of miles-per-gallon (or litres-per-km) [1].
[1] https://what-if.xkcd.com/11/
Well, if you want to be pedantic, it's litres-of-fuel per km-driven. That doesn't cancel as nicely, if you don't drop the annotations.
Arguably, we should probably use kg-of-fuel (or mol) instead of litres-of-fuel anyway.
> miles-per-gallon (or litres-per-km) [1].
The UK is metric except for distance and beer.
So the disgusting ‘miles-per-litre’ is presumably needed too.
Also the UK gallon is different from the US gallon. And the same applies to all the other non-metric fluid measurements such as pints and fluid ounces. Historically the UK gallon was used throughout the former British Empire (Australia, Canada, India, Ireland, Malaysia, New Zealand, South Africa, etc). By contrast, almost nobody ever officially used the US gallon except for the US (and a small handful of highly US-influenced countries such as Liberia).