Historically, cargo in AirlineSim is treated a bit a like a step-child. I mean that in the sense that it really should be there as it’s a crucial part of the industry, but the emphasis of the game clearly lies on pax operations.
I don’t want it to stay like that forever and the respective roadmap item exists, along with a bit of a discussion on the subject. The TLDR: A new cargo model for AS would have to take different kinds of cargo and the very much different structures of cargo ops into account, meaning a more or less complete departure from the current “cargo unit abstraction”.