[amb6883]

Corrugated cardboard can leave an imprint and shipping flat is a pain in the ass to do it right, with a much better chance of it getting damaged the bigger the print gets.

I have plenty of extra tubes so not having to ever buy any makes it much cheaper for me to ship with a tube versus flat. With tubes all I need is some kraft paper and tape. Shipping flat I have to use foam core (or some thing similar) and a mylar sleeve making it a hell of a lot more expensive.