Bk7 implies trade as a major flow, where Bk3 implies it's not a major impact on most worlds economies.
This is interesting.
Not being a Traveller historian, I'm certainly not going to challenge the "right" or "wrong"-ness of it.
But it does make an interesting puzzle as to why one universe would be trade heavy and another not so much.
It's easy to simply claim "There is as much trade as necessary, no more, and no less."
That is, over some unspecified amount of time with, effectively, unlimited resources, enough trade traffic will develop as is necessary.
If the largest ships are limited to 5000 tons, then the traders will operate the most profitable size and configuration of ships as possible. If that's 5000 ton ships, then that's what they'll run. If not, then something else.
Obviously, today, not every cargo ship is a monster sized container ship. But I'll wager that most are. For the types of goods that are amenable to be shipped in containers, I bet a large majority travel on these large ships, benefiting from the efficiencies and scale of the operation.
But if the Bk3 "universe" did not have much trade, it's just an interesting puzzle as to "why not". Perhaps the systems were so self sufficient as to only need start up materials and rare luxury goods. Why ship in some commodity when you can grow/mine/build it locally? Once the system is mature. In the beginning, then, sure, more trade may be necessary. Simply bringing in the bootstrapping goods. But then, the populations are probably lower as well.
Even on our little rock of a planet, we move manufacturing etc. all over the planet. We'd move the mining and such also, but unfortunately, the ore kinda likes staying where it is. So instead, we import labor to the mining site and export the material.
Heck, look at someplace like Iran. They EXPORT raw crude and IMPORT distillates as they don't have the actual capacity and infrastructure to meet internal demand for the finished goods.
Now some planets may well have exhausted their raw materials, and these would then become attractive markets for raw material.
Of course all of this revolves around the cost of trade. There's a baseline cost to trade -- the costs of the ships, crews, maintenance, etc. as well as the infrastructure to support them (starports, cargo handling facilities, etc.).
So, it's just a curiousity about "what changed" that made trade more viable and bigger in the post-BK5 TU than the Bk3 LittleVerse TU.