Snapedom

He was working with too many unknowns, thanks to his master (the white-bearded one). I suppose he should have kidnapped the trio from the Forest of Dean, held them in some secret dungeon at Hogwarts, Legilimensed Albus' lessons from Harry. (Or perhaps Severus should have threatened Ginny, publicly, to make sure he caught Harry. A bit dangerous, Tom doesn't like independent initiative.) Then once he was done swearing at Albus for the mess he created over the years, set off to hunt Horcruces as well as researching ways to remove a soul-bit from a living being while leaving said being's own soul in place. All the while preventing DEs from killing or kidnapping any students. Not knowing about the Elder Wand he wouldn't know how long he had until Tom decided to kill him. (Someone should write that fic.)

Who knows, maybe he was researching the Harrycrux problem in his spare time and didn't kidnap the trio from the Forest of Dean because he was not making progress, so the least he could do was not hamper whatever progress Harry may have been making in whatever mysterious assignment Albus left to him.