"The fact that" ... are you sure? They run 8 trains a day, on average ~3 car sets. Apart from an occasional spike in demand for a specific service, they are not usually especially busy. That doesn't indicate a route that has enough demand to justify competing services.
What is proposed is more of an intercity service with a few S&C stops though.
It doesn't really have any connection to the current S&C community railway operation.
There is very little population between Keighley and Motherwell to serve, and it's a long way. There's a small amount in Skipton and Carlisle, and some negligible amounts elsewhere. Accordingly you'd get some end-to-end between Leeds and Glasgow and very little else.
The end to end West Yorks/Craven to western Scotland passengers would be your mainstay though, and there are sizeable populations to connect. The lack of a direct high-quality road route West Yorks to M6 without making a detour all the way up to the A66 at Scotch Corner (unless a decent quality extension to the M65 ending at the A629 Cross Hills/Steeton bypass was built).
That also reminds me that the 150k in the Burnley/Nelson/Colne/Brierfield urban area would be another target market - Blackburn's only 15-30mins off Preston, but the stations in the Burnley and Colne area are 45-75 mins from Avanti services.
The driving/public transport time to Skipton would make interchange onto a west of Scotland service there quite attractive, especially if it was low cost like Lumo, or reasonably priced like GC.
Now, some people might use it to do walking trips to Ribblehead, day trips out from southwestern Scotland etc., but that would only be the secondary purpose of the service.
In the 1990s there was a proposal for a direct Leeds-Windermere service! I mean, I'd have caught it but I've no idea of the route it would have taken.
Presumably Leeds - Skipton - Bentham line - reverse at Lancaster onto WCML - Windermere branch at Oxenholme? The current Leeds to Morecambe services reverse at Lancaster, so it seems to be feasible.