Recently I noticed that the SK flight to BKK and SIN it not daily anymore, but 6x a week.

So they have trouble filling the seats. This is another sign for me that SK is not happy in *A.

Recently the story that they are happier code-sharing with CO to US.
Now no more sharing with TG.
Where will it end?

SK's product to BKK is the best. Way better the TG. TG can fly cheaper and has nice old 747's.
Code-sharing with then sounds like a stupid thing to do in the first place.

Only if you jointly operate a route like LH does will you win this battle.