I think they saw how many ppl were pissed that Triple H beat him at mania and said we won't do that again.
Not really comparable situations. Triple H was Sting's first WWE opponent, and not his retirement match.
People hated that shit because Sting had come in as basically the last guy of note who was never associated with WWE, debuted with a bunch of fanfare and then got beat by a notorious politicker who had nothing to gain at this point in a match that was basically all about re-exerting WWE's dominance over WCW. And the whole premise of the nWo being Sting's backup was pretty senseless too.
Match just kinda sucked as a whole and of course Triple H of all people beating him didn't help with the blowback.
No one except Young Buck haters would have really minded them winning. Most people expected them to win, and it woulda been completely reasonable.
I'm sure the call to have Sting win came down sheerly to the fact that Sting is such an unselfish legend, The Bucks are made no matter what, and TK just wanted to show his gratitude to him.