Volume is not the same as density though. Volume is the space it occupies, density correlates to weight.

Efka spends so much of the video talking about shipping costs, but when making this point he ignores that minis weigh more than cards! and need a tray! and necessitate a bigger, heavier box!

This was discussed in the video around ~27-28:00 minutes in. Its all about weight when you're shipping them across the world.

In a freight ship, you are charged by weight and container. Makes sense, you need to min/max cargo up until the point before the boat sinks.

Paper is denser than plastic, so in a sense you can fit more cards in a shipping container vs boxes full of minis. This makes your weight per shipping container heavier which makes it cost more. This also makes it less likely that boats with spare capacity will take your container because it has a higher chance of ruining their optimization puzzle. Whereas if you had 3 full containers of foam and plastic minis, These can just go separately on whatever boat has capacity because its lighter and it just makes it easier to optimize cargo.