My view is;
SAS is desperately looking for ways to increase revenue/profitability, and their CPH-BKK/SIN route is as far as I know - one of the best revenue-generating one.

My idea is that SAS does not gain too much from having code-share with TG. I think they want to try to fill up their 340's which have much higher capacity than the old 767.

TG is also quite aggressive - both increasing frequency and using large 747-400 aircrafts.

And they sell "Consolidator-tickets" in the Scandinavian market. I can imagine SAS with their "Rule the Scandinavian Market-philosophy" does not like their aggressivness.

I would guess (if the termination of code-share is correct) that it is something that SAS has initiated.

Again, just my personal ideas.