I don't know about BMW, but with Toyota, higher grades have preinstalled many options, and those same ones are made optional or offered as accessories for lower grades. For example: my Corolla hatch XSE has mudguards, hood insulator, etc. that are installed at the factory for XSE, and can be bought separately for lower grades. Limited C-HR came with mudguards, winter rubber mats, rear bumper protector, fog lights, 18" wheels, heated stg wheel, leather seats, interior flood lights, wheel locks, etc.As far as I know, these mud guards have always been an optional accessory and not factory installed. It's not uncommon for these types of accessories to be dealer installed options or at the port of entry/arrival. BMW has a few options that are installed at the port of receiving here in the States before the car is sent to the dealer.
And yes, especially in US, there are many regional distributors that make certain options/accessories like hood protector, door guards, wheels, tint, etc.