Yeah, cause Norman Osborne got killed by spiderman, so Osborne jr turned into a supervillain. And Brock jr got killed by Spidey, so his dad should attack Spidey. And since we're onto teh whole father/son-hatred-of-spidey-thing then we have to include Sandman's dying daughter. So sandman steals the symbiote sample from The Professor, unleashes it onto his daughter, his daughter turnis into SHE Venom and attacks Spidey. Because there's no better way of showing you hate Spiderman then showing your dad how to hate him too.
How about venom just takes over a new body? You guys are saying it like only a person named Eddie brock can be Venom. The symbiote can take over anybody it feels like.