It was a joke on the fact that

Cartons are not made only of cardboard, they're made of many layers of different materials. the innermost is a very thin layer of plastic (to waterproof the inside). So, the amount of plastic involved is surely less than bags, as most of the strength comes from the paperboard; but, on the other hand, being composite they're quite more difficult to recycle.
This, unless you have very different cartons (but I doubt)

 

I'm Canadian and I drink milk 13 times a day.
(out of a carton)

 

You're a freak for drinking out of a Carton.

 

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why not just dump the bag into it lmaoo.

 

Because:

1. you reduce air contact to the bare minimum;
2. you don't have to periodically wash the jug.

The more I think about it, the more it seems an actually very smart solution. But I wonder whether the bag falls out of the jug when you try to pour the very last milk in it? Is the jug, like, rubbery on the inside?

 

It's mainly just the condensation from the bag over time that generally keeps it from sliding out because it's so light at that point.

 

America has that too.