There was no one available. Konoha was still recovering from the war with Suna and all high-ranked ninja, including jonin and ANBU were sent to missions, either to guard the borders against possible assaults on weakened village, or to make sure the relations with other villages have not deteriorated, or to act as spies to predict potential attacks. Such are the consequences of war.
These tasks were more important than bringing back a 12-year old genin with psychological problems, so it's no surprising such a mission was given to a bunch of genin and chunin. Cruel reality, I know, but that's the way it is. U_U
I doubt any mission they were doing outweighed the importance of preventing an S-ranked criminal who hates Konoha from obtaining what was probably the village's most powerful Kekkei Genkai.
The risk for the village posed by Sasuke's betrayal was only potential and even if it was to happen, it would take years before Orochimaru could accomplish that. Jirayia knew about it, so Tsunade likely knew it as well.
The danger of the village being attacked, however, was very real and it could happen virtually any moment.