So, this is an issue which comes from CT and MT....Not Mongoose
And it has absolutely nothing to do with trading, though trading will be blamed
Ultimately, when you land in port and those members of the crew start working on selling the cargo, cleaning out the passenger staterooms and the going out shopping, cargo hunting and seeing the sights....
The ship's Engineer (or engineers) have work to do.
In fact, they "Always" have work to do.
After you lift from a world and burn for the 100d limit - you make a jump.
After that, the engineering staff have time while the maneuver drive is off line to spend the week in jump doing minor maintenance
As soon as the ship exits jump on the other side..
1) The engineering team have to bleed off the jump capacitors and begin maintenance and reset work on the jump drive
2) After the ship makes port - and assuming it is berthed in an internal space where the ship's systems can be powered down, the team have to begin maintenance on all that. Power plant, jump drive, live support....etc.
A ship is not a ground car, which can be put on a lift every few thousand miles.
This is the thing that is either gonna be well maintained and kept working by a responsible engineering team
Or it is an less than well maintained craft which will suffer break downs which can damned well kill you all
Now, based on "That Scheduling".....the trade system has been "1 Roll per week in port"
Which is why the trade system gets the blame