I think one of the problems in this case was the rerouting to CO. CO is not their close partners and it probably costs them to reroute you to them. Their original plan was to use their own flights for you and it wouldn't cost them any money kind of.

And why would they inform you ver well in advance? So that all the passengers would have opportunity refund their reservations and SAS would lose even more money in the end?

This is game ... good that you managed to get everything sorted.