I don't think it was so much labour taking scottish voters for granted , more the SNP realising if they could secure the support of the veterinary favour of independence they would be untouchable, if around 45% upwards can be persuaded to vote on a single issue you couldn't lose the seat.
It's the same with brexit, that's what johnson and Co tapped into.
A good chunk of the population are not interested in the vast number of polices but if there's one they can nail their colours to the mast the other stuff doesn't matter.
Pro independence first the rest isn't that important
Pro brexit first the rest isn't important.
Iam seeing many tories saying the fact that their Wakefield candidate wasn't Pro brexit cost them the seat.
That's the problem labour have, moving the issues away from brexit/independence