Kirkby was probably seen as a logical terminus for electrification. Traffic potential between Kirkby & Wigan is not huge.
The next station, Rainford is inside the Merseyside area, but the station, formerly Rainford Junction, is poorly situated for most of Rainford village - about one mile from the centre, and has a tiny car park.
Next comes Upholland, the station actually located in Pimbo, which is little more than a row of houses; the main part of Upholland is over a mile away and has no bus service to the station. Also there is very little space to park cars here - no formal car park.
Orrell station is better situated, but Orrell is not huge, and also had a good bus service to/from Wigan. .
Pemberton station is near the edge of that place, and has to compete with fairly frequent buses into Wigan which pass closer to most of the housing & shopping areas of Pemberton.