The advantage of a SMPC-enabled oracle is that is impossible to tell how the participants voted. So you cannot bribe the participants conditionally on how they participated. This attack works because it bribes either everyone or no-one.
An attacker credibly commits to pay every participant in the oracle dependent upon the outcome being wrong.
The reward for being in majority is R, and the attacker's bribe is b.
|vote honest |lie
wrong outcome | b | R+b
correct outcome| R | 0