You've never left the US, have you? No one uses 3.8 liters of gas, they obviously use 1 liter of gas, or 10 liters of gas. Most cars have about 40 or 50 liter tanks, and gas is paid by the liter.
Juice is also bought by the liter, usually in 2L bottles for a family dinner, or 500mL bottles for one person alone.
2l is very large in my (Dutch) idea. Orange juice in my country is typically sold in 1l cartons and more recently also 1.5l. But the latter only for the most popular flavors. The same is true for milk.
I think I should have soda 'soda', not 'juice'. Here in Romania, things like orange juice and milk are also usually sold in 1l bottles. It's things like Coca Cola and Fanta that are typically sold in either 0.5l or 2l bottles (even 2.5l around holidays; but 1.5l is also becoming increasingly common).
It's common in the US and Australia and, I suspect, any large producer of fruit with a normal culture of drinking juice. Anywhere that imports 1l seems to be more the norm.
Strange what you say about milk though - I've usually seen the 2l form factor anywhere westerners are common. Could be a local convention?
The EU had rules about standard sizes for most packaged food, which probably influenced this. I can't find what they were for fruit juice -- the rule was abolished in 2007 (or 2002?), since surveys showed people who cared about the price would look at the "per 100mL" indication on the shelf anyway.
Different European countries produced different fruits (citrus, apples etc), but I've not noticed that e.g. apple juice is in larger containers in Britain, and orange juice in Spain. If anything, the trend is to smaller containers, for variety and health.
And have you seen anywhere people using 3.8l or 0.334 meters or 12.5cm as common measurements? Or in general, people having problems with expressing quantities in simple multiples or fractions of liters, (kilo)grams, and meters?
I do understand that it is hard to adjust intuitions from one system to the other, but I can't imagine how someone can think that people have problems using the measurement system they learned in primary school.
Juice is also bought by the liter, usually in 2L bottles for a family dinner, or 500mL bottles for one person alone.