What is actually delaying the line into Skelmersdale, does anyone know ?
It has to go through the time-consuming GRIP process to ensure it is value for money and feasible. The current state of play seems to be that an outline business plan is being developed to be delivered to the Government to try and secure funding - see this report from LancsLive (from May 2019):-
A train station for Skelmersdale has moved a step closer after it was agreed to move to the next stage of the process which could eventually make it a reality.
Lancashire County Council’s cabinet has approved a plan to commission an outline business case which will then be put to government.
The document will determine whether a town centre station, connecting to the Wigan to Kirkby line, would be affordable, deliverable in a reasonable timescale and value for money.
An estimated cost for the project had been expected in March, but further work to decide the most suitable power source for the route means the figure will not now be known before the end of the year.
Building a station at Headbolt Lane could be a useful stepping stone, as the costs of the station would presumably include the works needed to reinstate a double track line through Kirkby and extend the third rail. That reduces the amount of work that needs to be paid for out of the Skelmersdale project's budget, improving the business case for the latter.