In your case, there are three main categories of reason as to why interplanetary shipping would use space docks in orbit to drop off goods as opposed to consistently dropping onto the planet with loads of goods
#1: Transit Logistics
As somebody that works for a courier, the courier does not have a truck for every delivery location going to every other delivery location in the area. That would be way too expensive, incredibly inefficient, and be a terrible use of resources. Instead, volume is sent to a regional hub where volume from the region is aggregated and processed in bulk far more efficiently before it is sent to where it needs to go.
Should it need to move outside of the country of origin, it goes to a designated export location and leaves the country from there, also consolidating points of exit (and entry) from the country. The only exception to this is if the origin and destination locations are the same -- they will leave it in the building and deliver it the next day most likely.
Couriers and post offices alike will do that. Those hub points are likely to be in the larger centres where there is more population (and volume to move) and good transit options to move that volume. Major regional cities are the order of the day, likely the largest city in the regional area.
This relates to your scenario in that your spaceport drop-offs are the regional hubs in this scenario. Your shipments will go into these space hubs and be processed by workers in the station. From there the volume will be distributed planetside in whatever way that particular planet handles incoming shipments.
Yes, this is trading goods and not mailing packages, but a similar premise of hub and spoke still applies -- a large enough company will have a main distribution outlet, and smaller ones in strategic locations to service customers readily.
Space has a whole lot of nothing. It is much easier to accelerate a mass to speed, cruise for a bit, then decelerate back to near zero to dock with the spaceport.
In contrast, planets have gravity, and atmosphere to get in the way of everything. It takes fuel to push through all of that. Not only that, but every planet will be slightly different.
Some planets will have a higher (or lower) gravity. Different planets will have different atmospheric conditions -- some conducive for blasting out to space, and others less so. Some planets might even be actively dangerous to the pilot or the vessel. It's all so complicated overall having to keep track of what planets are safe to enter, what ones will kill you on entry.
Each world may even have their own planet-based spaceship standards, meaning that some places might not be possible to land because your spaceship is incompatible with their landing and/or launching infrastructure.
That does not even take into account the bio-hazards that might be brought into or out of the planet by accident. The liabilities around invasive species has got to be immense once you deal with an entire planet that may not have any form of defence against one.
No, better and cheaper to dock at a spaceport and let the planet's administration handle all of that mess and cost. Less expenses for the shippers/merchants in fuel to launch from the planet and lawsuits in case something went wrong with a planetside delivery. Plus, you can save some money on spaceship designs with some parts being universally compatible for docking with space stations.
This holds true with larger suppliers as well as the little independent agents.
#3: Game Logistics
AKA: Conservation of Details
If you are making a game about space deliveries, then do you need to know how the planets operate between the space station and the ground (or water) itself?
I would argue that if your game is about interplanetary mercantile logistics, there is no need to worry about how they either land imported volume or lift up exporting volume. The only other thing you really need to care about is what they would import and/or export. Of course, the other details of the game may change that.
The player isn't landing on the planet so they will not have to know the amount of fuel needed to land, or the shielding needed to survive entry onto the planet. All players will need to know is that E Resources are available per T time units and that they can process I units in delivered goods per T time units. Possibly with needing to spend Q time units in quarantine due to laws.
What you need to know is reasonable numbers to fill in the variables dependent on each planet. This might be the topic of other questions -- I would recommend a search to see if you aren't repeating a question. The Tyranny of the Rocket Equation is almost as well known as the Tyranny of the Square-Cube law.