Now, The Venom Site has revealed the original plan had been to have Carnage as the main villain in the first movie itself.
In the movie, Carnage appears to be one of the symbiotes that landed on Earth alongside Venom instead of being its offspring.
The movie established the character of Venom as a popular anti-hero, and also set up a sequel where he would battle his own offspring/arch-enemy Carnage.
Having Carnage as well as Venom would have provided added incentive for fans to give the movie a chance.