FR will allocate their new deliveries to where they think they can make the best returns and as they have said, LPL is not that place for them at the moment. There's nothing to say they won't put more aircraft into LPL in the future.
MAN and LPL are separate markets but due to the geography, the catchment area overlaps quite substantially. MAN is where they are putting growth into at the moment so understandably LPL is not going to be their next priority for growth.
At least they are able to pretty much maintain the size of their operation in LPL whilst putting growth into MAN unlike certain airlines who only seem to cannibalise one airport at the expense of growth at another.
When you look at the north or north-west region overall (including say LPL, MAN, LBA) FR has brought a fantastic amount of growth over the last few years.