Some countries back in the 70's had obligatory fog lights, didn't the UK?
If so, or even if not, it could be that bmw anticipated on them becoming standard, so they opted to already ensure lthe provision was there.
When i was working with Volvo around 2002, one of their car model had a 3rd brake light when no-one else did. Explanation to the world was that they were leading safety. (which they did!).
Reality in the engineering dept was that we had to make a guess when the legislation made the 3rd brake light mandatory. We guessed wrong; it wasn't for another few years