If you believe the ORR figures for useage, the Windermere Branch is surprisingly low. I tend to compare stations to my home station Rye on Marshlink and it suggests that passenger figures are about a third of Marshlink which is run as a basic hourly dmu service. Of the 300k that use Windermere every year approximately a 1/8th are captive to the branch only travelling to Kendal. Likewise why are London to Glasgow trains stopping at Oxenholme and Penrith making the London to Glasgow services uncompetitive time wise now there is a regional express service from TPE?I think this goes right back to introduction of the VHF service that came in in Virgin days and several services such as the ones you are suggesting were removed. And in those days the units trundling up to Windermere would only get 75 top speed. Not these modern 195s. So making windermere/cumbrian coast passengers interchange usually works. But not on this occasion.
It's frustrating that right after covid the Avanti 'do not board our service without a seat reservation' quietly forgot this interchange. Another example of the disjointed railway system .
I can quite understand why Avanti dont see these stations as a priority during disruption.