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.
Strange what you say about milk though - I've usually seen the 2l form factor anywhere westerners are common. Could be a local convention?
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.
https://ec.europa.eu/growth/single-market/goods/building-blo...