Reason: The kingpin pissed off venom. He is paying the doctor and Shocker big money they both need badly to kill him. Venom is so pissed he is willing to kill them (not that he would need any motivation anyway). No one gets the drop on anyone. Shock and Ock walk out of Fisk towers to intercept venom on his way in (takes the ground floor to ensure he would have lots of guards to kill on his way up to fisk).
Venom sends out tentacles to hold Doc Ock’s arms and kills him quick. Then takes his time killing the Shocker. Electricity does not hurt Venom so what can the Shocker really do to him?
That is what i thought but i was looking at some old threads with the shocker and venom in them and shocker always got owned. I didn't understand because i always thought he sent out sonic blasts which would totally mess with symbiots!