I do nit think about transferring module in severel flights

wint 1 tn cargo.
What @Lestat is referring to is that our ships use cargo ranks which hand cargo in standardised one tonne containers. So a 32-tonne cargo module can carry 32 containers - but cannot transport a single item of two tonnes mass.
Compare this to standardised shipping containers used today, which allows any cargo to be handled by standardised equipment in any port.
So to transport a multi-tonne item using Elite's cargo system, it must be broken down and packed in these one-tonne standard containers - otherwise it couldn't be handled, loaded, unloaded, or stored, by the port facilities.
Furthermore, once broken down each container would have to be a unique cargo type, because they could the be split, lost, mixed-up during transport, and you need the full set to have any chance of reassembly (can't rebuild a car from four tonnes of tires...).
Not that most things could be divided up in the first place - did you cut the engine block in half for transport, and expected it be able weld it back together? Typically, even for items that could be disassembled, the cost of this and reassembly far, far exceeds original cost.
Our experience in Elite is only of small scale trading. We know that bulk transports (Lynx?) exist - using a different scale of containerisation, and handled by a different set of port facilities. These are what is transporting ships and module for us, but we don't have access to such ships (yet??).
It would clear up a lot of confusion if FD added these mega-transports as NPC ships or scenery that was at least visible in the game.