I thought there used to be a LIverpool to Edinburgh/Glasgow service many years ago. Did it not join with the corresponding Manchester to Scotland service. I don't understand why Liverpool has been effectively isolated from the cross country network. Years ago there was also the Liverpool to North Wales loco hauled service. I know there are plans to reintroduce this service in the future but it's been described as a service improvement when it's not an improvement in simply reinstating what there was before. Same with the Blackpool to London services.
The Liverpool - Scotland service was never high frequency, and was steadily reduced and made less attractive to passengers. From a selection of timetables:
1975:
07:38 Liverpool - Edinburgh (arr. 11:55)
(connected at Preston with Man. Vic - Glasgow service)
09:41 Liverpool - Glasgow (arr. 13:23)
12:41 Liverpool - Edinburgh (arr. 16:50)
(connection at Carlisle St. Pancras - Leeds - Glasgow)
17:40 Liverpool - Glasgow (arr. 21:36)
(connection at Carstairs for Edinburgh)
08:00 Glasgow - Liverpool (arr. 11:46)
12:35 Edinburgh - Liverpool (arr. 16:47)
16:40 Glasgow - Liverpool (arr. 20:30)
17:55 Edinburgh - Liverpool (arr. 21:58)
1984:
07:43 Liverpool - Edinburgh
(Joined Man. Vic - Glasgow portion at Preston)
09:30 (Summer only) Liverpool - Edinburgh & Glasgow
16:20 Glasgow / 16:10 Edinburgh - Liverpool (Summer only)
18:10 Edinburgh / 18:20 Glasgow - Liverpool & Manchester.
1999:
17:00 Liverpool - Edinburgh (arr. 21:11)
06:27 Edinburgh - Liverpool (arr. 10:53)
So, not only a worse service, mostly at times not very convenient for tourists, and slower than in 1975. Hardly surprising that Liverpool / Scotland services became unattractive.