A lot of products are “intermediate”.
A lot of producers of said intermediate products aren’t exactly selling (or buying) them. I make a ton of HER for KOM and FIM. 10% of it ends up on the cx, maybe. Compare that to the volume of KOM which is publicly traded, it’s pitiful how much HER is publicly traded.
Apply this to many other common intermediate products that aren’t T1. THF, DDT, BGC, BCO, if you’re gonna bother making these, 95% of the time it’s because you internally have a consumption requirement for it. And maybe, maybe you’ll sell some of the excess on the CX.
This is how the entire high end of the market works. There aren’t really strong incentives to not vertically integrate the entire production chain. Or work with one other key player who compliments you, especially when dealing with high tonnage\volume production chains on a single world. We don’t see much LIO or HAL being publicly traded. HAL is consumed on-world to make CL, same for LIO to make LI.
So - what we end up seeing is by far the most commonly traded items are base commodities like Hydrogen or Oxygen. T1 items. And finished production chain goods. All of the consumables. Prefabs. Consumables for ships and the like.