Obviously you should know what the world is like before your players go there. The invocation of MOARN was saying it isn't worth documenting whether it's the 100D limit of the planet or the 100D limit of the star that is causing your 6-12 hours of travel to the starport. When its 36 hours travel to the starport that matters.
As far as the "why it takes a week in system" if you want to decide that, you can do so. But that's not how it is written to work. The crew is not actually on vacation during port stops. Maybe if you are a corporate trader with established contacts at this starport, you can arrange everything by comms. But PCs generally aren't. They are itinerant traders scrounging for cargos that the big leagues don't want. They are not getting priority service at the port, because they aren't paying for it. Unless they are. No one is sitting around saving cargo for them. They are trying to track down people who can't/won't book on a real trader. Either because it's last minute or their paperwork is bad or the cargo is some annoying thing that isn't containerized or they can't afford the rates charged by real shippers or whatever.
The same thing with passengers. They are getting people on standby, people who are having trouble getting tickets on the scheduled liners.
Or they are at a some backwater port with no services and the passengers and cargo are probably scattered all over the city waiting for that once a month surprise ship to turn up.
So the assumption in the game is that it is going to take time to make all these arrangements, to do the maintenance yourself, to buy supplies, to vet these deals you are making, to herd the cats into getting whatever you managed to scrounge onto your ship. To make sure that online broker you signed up is actually legit.
You don't have to play that way. You can make the starports fawn all over the PCs and give them prompt, efficient service. But that's not the way that the default setting operates. It assumes that the players are having to actually bust their humps to scrounge up cargos and having to put up with suboptimal arrangements as a result.
Is it different for big corporations? Of course. But even with all that arranged, they don't want to spend days in real space. Its a waste of money and throws off their staffing calcuations. IRL, merchant mariners often have schedules that are like 28 days on/14 days off. Because they are on the ship for 28 days straight, then they are off for two weeks. So either their ship has 50% extra crew that rotates or they move between ships of the same company operating out of that world. Days in space count as days in space whether you are making any money or not. And an extra 4 days between ports is not making money.