Airlines often drop routes that dont make them any money! its obvious!
Passenger figures on the AMS were low - very often about the 60 mark, sometimes not even that. There will now be 3x 737 and 2x 757
The reduction in freq on the KRK is only becuase they have upped the operated aircraft to a 757. Jet2 have dropped various routes in the past, as have easy and ryanair as well as EVERY other airline going, its what you have to do to keep your business going, I wouldnt worry about Jet2 leaving NCL, there are so many strong rumours of long haul ex NCL and chater destinations like SSH PFO and LPA so i wouldnt expect to see them going anywhere soon.
Jamesair - not to sure about the time changes you mentioned, AGP n PMI are not changing, however 1015 LGW is moving to early afternoon which should be better.