Indeed. Hence why the route has minimal value to any long-haul passengers. And why that's not going to be changing for the foreseeable future.
Reinstating the direct CrossCountry services between Glasgow and Leeds would offer better journey times anyway if that were the objective.
No. Although I'm not sure what difference it would make if they could, there's no rolling stock for this.
Do the Liverpools to Scotland run with capacity? If they do, combine a Liverpool-Glasgow and Manchester-Glasgow at Preston as it used to be. This will allow 5-car trains to continue using Manchester Airport station, still allow seats for joining passengers and free up a path on the WCML north of Preston every two hours. The freed up path could be used for a Leeds-Glasgow via Carlisle through service.
Carlisle might be a hub, but it is well known that passengers prefer through trains, especially elderly, disabled and those with pushchairs and/or heavy luggage. Not easy travelling northbound where the connection means crossing over the footbridge.
Booking a ticket From West Yorkshire to Glasgow, you are automatically routed via Newcastle and Edinburgh with a change at Edinburgh. Passengers would gravitate towards a through Leeds-Glasgow train via Carlisle if there was one.
If they are able to, many Harrogate residents prefer to drive to Skipton and use that route even having to change at Carlisle instead of via Edinburgh necessitating a change twice at York and Edinburgh.