I see the point that you're making, but there's only one set, so they appear to be basing their finite resources on two points:
1. Given the relative populations of West Yorkshire vs Carlisle, the main market will be people from the southern end of the S&C wanting a leisure trip to the countryside
2. The A-list bit is the Settle - Kirkby Stephen section (Ribblehead especially)
...so, you focus your resources on running as many return journeys as possible over the most interesting/lucrative section, whilst starting at the southern end and finishing at the southern end (given that good connections exist at Skipton to/from Leeds and Bradford - though not Colne

).
Running all the way to Carlisle (or Leeds) would take a long time - you'd be talking a couple of hours if you did a round trip from Appleby to Carlisle - so if you are trying to attract Carlisle passengers you'd need to start at Carlisle before lunchtime and have a return back to Carlisle in the afternoon, which would come at the cost of trips over Ribblehead (and maybe then makes the start at the Skipton end too early to attract the "leisure" crowd - especially if they are coming from suburban Leeds/ Bradford in the first place).
You don't have to stay in Appleby all day - there's an onward coach service taking you into the Lake District to supplement the train.
This isn't a normal kind of service, it's not intended to be one - I don't think that many of the leisure market passengers will be too fussed about which particular diesel locomotive pulls it (though I love a large logo 47) - I guess it was conceived in the pre-Covid days as a way of attracting the "thirty - fifty quid day out" kind of leisure passenger who'd otherwise be going to the zoo or some National Trust property or maybe something like the NYRM - but this way Rail Charter Service can provide all of the highlights of a preserved railway (leisurely trip on heritage stock, stunning scenery etc) through the key summer holiday period without the need to maintain dozens of miles of heritage line all year long like the NYRM etc have to - simply piggy-back onto Network Rail infrastructure and appeal to people who'll pay a lot more to ride over Ribblehead than on a Sprinter.