[1] https://sacramento.cbslocal.com/2018/06/08/new-california-wa...
Top loaders were popular in the US for a long time, and they generally fill all the way up.
I have a top loader (a Whirlpool from 2011) and it most definitely doesn't fill "all the way up". It uses as little water as a modern front loader and also adjusts the water level based on fill level.
I am afraid that is physically impossible, unless you are washing a single pair of socks.
This also typically allows for a larger drum.
* Top loader - 4.4 cubic feet, IWF 6-1/100
* Front loader - 5.0 cubic feet, IWF 3-1/5
Not knowing what those meant, I looked it up. The "water factor" represents how much water a machine uses, in gallons per cubic foot of capacity. In other words, the front loader uses about half the water that the top loader uses.
As another commenter said, top loaders are different in the EU - in North America, the whole drum is turned on its side and water must fill as far up as the clothes go - there's no tumbling action to shift clothes in and out of the water at the bottom of the sideways drum in a front loader (and a European style top loader)
Now the modern washers don't trust you to make the proper selection, and often don't get your clothes completely wet.
I've never had an issue with modern front loaders not getting my clothes wet. They are much better at spinning them dry at the end, though.
I think the big thing that is different in the current top loaders, vs the old ones, are some don't have an agitator -- instead they use a low profile impeller at the bottom to force water vertically. And the ones with an agitator have the impeller shape at the bottom, so there is still vertical water movement.
The front loaders started to go out of style, partly because people complain about an oder build up in them. Not sure what that is about. And worries about the seal in the door leaking (if the float gets stuck and it puts too much water in it -- my brother has that issue periodically).
I would think that a good top-loader design would be something that has a pump at the bottom (under the basket), and circulates water to the top and sprays it down on the clothes. But I haven't seen any like that though.
Your source does not call this the average, but the upper limit. Washing machines have a range of sizes you can set them at ranging from small to "super-max". Also a range of durations depending on how many cycles and how much washing is needed.
You'd need to relate it to how much laundry gets washed per gallon.
Also, some parts of the US are semi-tropical and even swamp. Not every state is as worried about conserving water.
Or it could be use of liquid detergents, which seem to be more common in the US. My washing machine's manual specifically warns not to use liquid or pod detergents, and they lead to internal buildup.
Washing machines are in a weird place where they are expensive to replace, but parts and labor to fix them when they break is almost, if not more expensive.