Ivan
I'll speculate that it'll be that same word again - YIELD.
Whilst many may moan at the lack of a winter MAN-NCE service there must be a lack of overall need. As you say, easyJet operate from LPL, perhaps that capacity is all that is needed from the NW in the winter. If there were to be a service from MAN too that might well split the load factors making neither operation worthy and soon there'd be none.