Okay, so one of the key parts of Traveller as a game is the importance of high-population worlds. For most gamers, they will be involved with interstellar trade and most of the demand for such goods comes from the billions of people who live on high-pop planets. These worlds are also where the majority of the citizens live, where the majority of the taxes come from, and are strategic choke points in an regional conflict. For Kobra Worlds, the region was hit heavily by the Collapse so only a few high-population planets exist, most notably on "Earth Prime" worlds. Also, if you notice, more a third have lost their main starport and only a handful break TL10, the rest are fairly low-tech worlds but just because you are low-tech doesn't mean you don't import off-world goods! In fact, I would think that demand for high-tech goods for the billions of people on low-tech worlds would be in huge demand, but your mileage on this issue may vary.