Don't know the exact answer but generally, it's due to the weight of the vehicle. Some models may have more optional equipment that adds weight to the car, thereby reducing the load carrying capacity. Higher end models will generally have more equipment/options so all things being equal re: the suspension, will have lower load capacity.
The port installed accessories. I have one on my 2020. The body side moldings, door edge guards, etc.
I was going to say dealer installed accessories, but I'm sure they would be required to add such a label.
