At a guess it has something to do with needing to withstand 70+ mph winds. There needs to be considerable force holding the door against its seals at all times, and in a mechanical latching system this force must come from a spring, which must be charged with energy via a good slam.
However there are minivans with electronically operated sliding doors, which either power the latch allowing you to gently close the door, or (going further) powering the entire closing operation at a button push. I surmise the reason we see it moreso on minivans is because 1) it is particularly difficult to work up enough energy to properly latch a sliding door, due to losses from the 90-degree change in direction at the end, and 2) violently slamming the sliding doors on a minivan is very dangerous to children's fingers.
It's not about wind pressure. It's that the door when properly closed becomes an integral, load-bearing part of the car's structure. In the event of a crash or rollover, an incompletely-closed door makes the car much weaker and less protective of the occupants.
It's about wind pressure only for doors that have the hinge at the back (I think those also have safety systems that prevent them from being opened while the car is moving). For the more common ones that have the hinge at the front, wind pressure will actually keep the door closed.
I'm not sure I buy this - how is load being transferred through the door? Surely not through the rubber seals, those have minimal shear strength even when compressed. That leaves the hinges, which are certainly robust enough, and the latch, which unless I'm mistaken is only designed to secure the door from opening (usually they engage with some sort of rod or peg, which can't transfer torsional or axial force (i.e. the latch is free to slide along or around the peg).
Luxury cars like MB and BMW also have a soft-close door mechanism for the normal driver and passenger side doors. There's a cam that pulls it in the last few centimeters.
I'm not sure how much money I'd pay for it, but it's a nice feature.
> I surmise the reason we see it moreso on minivans is because 1) it is particularly difficult to work up enough energy to properly latch a sliding door, due to losses from the 90-degree change in direction at the end, and 2) violently slamming the sliding doors on a minivan is very dangerous to children's fingers.
There is also a third, dumber reason, at least for cargo van slide-doors. The surface area of sliding doors are large. When the door takes that 90 degree turn and moves very fast towards the vehicle, it is pushing a lot of air into the vehicle. The air in the vehicle has nowhere to go, so it acts as an air-spring, slowing down the door. To properly latch the door, you have to really slam it hard. If the windows are down or an other door is open, the sliding doors latches very easily. I thought I was going crazy when my door was closing easily ... sometimes. Some cargo vans even have vents that allow air to escape, but people tend to cover them because they don't know what it's for. But electric sliding doors also solve this problem, by moving slowly and letting the air escape.
TLDR: if you car door doesn't close, open the window :)
However there are minivans with electronically operated sliding doors, which either power the latch allowing you to gently close the door, or (going further) powering the entire closing operation at a button push. I surmise the reason we see it moreso on minivans is because 1) it is particularly difficult to work up enough energy to properly latch a sliding door, due to losses from the 90-degree change in direction at the end, and 2) violently slamming the sliding doors on a minivan is very dangerous to children's fingers.