On the topic of the sound team being cultivated and the amount of effort Orochimaru put into them... remember, this year's exams were not normal. There were two jinchuuriki, Konoha's most talented rookie generation, and several completely OP bloodlines.
Take that out, remember the skills displayed by the sound team, and it's not hard to guess that in a more normal exam? They'd easily have been finalists, possibly the overall winners. And doesn't that sound (no pun intended) exactly like the sort of thing Orochimaru would do to twist the knife? Having a new village come out of nowhere and humiliate Konoha on their own turf, right before he kills his target and smashes them; just one extra sadistic punch to the gut.
Put in that context, the way he treats them after they lose actually makes a fair bit more sense. He's not just getting rid of them because they lost, their losing is a personal failure on his part- the team he set up to humiliate Konoha being defeated humiliating themselves. Better cover it up and forget about it as quickly as possible.