Well, has anyone ever actually canvassed local residents if they want to replace their fast service to Victoria, that currently takes less than half an hour, with a very slow tram ? I've not seen anything to suggest this is the case. Then there's the fact that the Atherton line isn't some branch line, but is an integral part of the railway network to Southport and Kirkby, so isn't really suited to being hived off
I'm not aware of any canvassing,
but the Oldham Loop seems to be a fairly similar case.
That went from four trains per hour into Victoria to five trams per hour into the heart of Manchester (later increased to ten trams per hour), so seems a fair test of whether the people of Atherton would swap a couple of trains per hour into Victoria with five trams per hour into the heart of Manchester?
Maybe the trade off is worthwhile and people would prefer a frequent service that avoids the need for a long walk through Manchester City Centre to a faster (but less frequent) service that dumps them at Victoria? There's merit in both options, but the Great Mancunian Public seem to prefer frequent trams.
I'd say "faster", but the Atherton train takes around half an hour to cover around ten miles - it's not great, is it?
Okay, you could throw money at the Atherton line to improve it but it's never going to get much of a more frequent service, given the well documented problems squeezing trains through central Manchester and the imbalance (since lots of services from the "east" terminate in the shed at Piccadilly, and the horseshoe shape of the Ordsall Chord) that means we have too many services from the "west" (compared to services from the "east" able to run through to the other side of Manchester).
Any path (through Salford) for the Atherton line would have to be fought against bigger destinations (Liverpool, Preston etc), so even if additional paths were found there's no guarantee of Atherton ever getting a more frequent service.
Whereas, a tram could be a lot more flexible, there's scope to run trams that properly serve central Salford en-route, actually extend into Atherton (rather than the current station that's half a mile from the centre of the place). Look at how the flexibility of light rail has allowed trams to serve central Oldham/ Rochdale properly? Trains could never have realistically done that.