DaveReidUK
Probably because that's the part description as per the drawing as well as what's in the engine/overhaul manual.
The PW4000 series is a 2 spool engine with a fan (LPC 1) and 4, 5, 6 or 7 additional LPC stages depending on model:
Historically LPC blades have been labelled with the fan being number 1. Not sure if that's the case with modern high bypass ratio engines, but it makes sense.