However, as far as I can make out, the 'pull switch tradition' is by no means 'rooted in' BS7671
It originated there but isn't a requirement. It's probably due to someone in the distant past 'interpreting' the regulations in a particular way, making some recommendation, and from that point on it became 'the regs' even though it wasn't. A familiar story that is repeated to this day.
This is regulation 405, from the 1955 13th edition, regarding switches and controls in bathrooms:
Nothing there requiring switches to be pull cords, or outside the room. Only that they must be out of reach, which is equivalent to the zones in the regulations today - outside of zone 2 is 600mm from the bath, which for most people is out of reach.
The rest is also remarkably similar to today, with no provision for portable appliances (i.e. socket outlets), and lampholders having protective shields.
Regulation 314 referred to there looks like this:
so for appliances installed in bathrooms, the choices are a fixed pull cord in the room, or a switch outside the door of the room.
Note that this is for appliances only, the whole of 314 being applicable to non-portable appliances.
The definition of 'appliance' in the same regulations is this:
and that definition specifically excludes lighting and motors.
Therefore if a switch was in a bathroom and it controlled something other than a light or motor, a pull cord switch was a requirement. The alternative being a switch outside the room adjacent to the door.
For lighting, normal switches were allowed in the room, and have been ever since, and still are - provided they are out of reach of someone in the bath, or in the more recent editions outside of zone 2, which amounts to the same thing.
If people really want one, there is nothing to prevent pull cord switches being used for lighting in bathrooms or any other location, but it is not a requirement and never was.