The Leigh loop service had been increased to (mostly) hourly when DMUs were introduced on lines in that area. However, the pre-diesel services had been so poor that usage had declined to low levels, and they (BR - and the Treasury, who exerted strong influence over BR finances, and who were probably largely "pro-road" on transport matters) - failed to allow enough time for passenger traffic levels to improve after dieselisation. Also, due to mining subsidence, semi-permanent speed limits made the services rather slow between Ellenbrook, Tyldesley & Leigh.
Wigan North Western to Manchester Exchange via Tyldesley & Eccles was also badly affected by subsidence, and apart from Tyldesley, the intermediate stations were "less than ideally" situated relative to population centres. For example, Hindley Green had (and still has) no obvious centre of population; much of it is a "long thin" settlement along the A577 road, parallel to the railway, with a station that could only be convenient for a small fraction of the residents.
Howe Bridge served a smallish suburb of Atherton, nearly a mile from the town centre, whilst Platt Bridge had to compete with high frequency bus services to/from Wigan. The local rail services were steadily run down until they became near-useless, and the faster services largely duplicated the faster, more frequent services between Wigan Wallgate & Manchester Victoria.
(Slightly OT - Hindley Green is effectively an eastward extension from Hindley (town); and none of the stations (present or past) claiming to serve Hindley (or Atherton) are / were particularly convenient for the town centres of those places.)