he summoned the 4 kages

and as a Sasuke fan there is no way Sasuke can beat these 4 kages + Orochimaru with full power
( i'm not like itachi and madara fanboys who think that their favorite character can beat 4 kages and Oro in the same time )

so this is a golden chance for Orochimaru to finish off Sasuke and take his body

maybe because a plot

who knows