My impression is that they basically entirely collapsed in ways that were mostly self-inflicted and boil down to "Don't you want a free Scotland?! Wait, what do you mean you want a free Scotland *with politics meaningfully different than England's?*"
Kind of like how I always felt that Labor wound itself up the political woods for years following Brexit:
If you want to be an effective opposition party, you have to present yourself with policies that are IN OPPOSITION TO WHOM YOU'RE RUNNING AGAINST!
