The point of Labour is to end austerity and build a society fit for the 21st century.
I agree with your reasons but i'd place more emphasis on people in the North East feeling they don't share common cause with the Central Belt. Fishermen and farmers basically want an MP who they feel works for them and provides more quotas/subsidies.
It's not possible to appeal to every constituency in Scotland but the SNP have to try. This causes them serious problems when creating policy and probably explains why they have expended so much political capital on crazy, doomed to fail, schemes like corroborration and named person.