Ock was a good scientist who became a murderous madman hell bent on completing his life's work at any cost, and who redempted his evil at the end. His theme fitted in with Peter's of giving up what you want the most to do the right thing.
The Lizard is a good scientist with a family, who tries to regrow his missing arm, and becomes a beast who kills people, who gets cured eventually. Plus, he's a friend of Peter's.
There's a difference. Ock was a scientific idol to Peter, like in the 90's cartoon show. Connors is a friend. Two different stories. The only similarities is that both were good scientists . But then so was Norman Osborn until the performance enhancers screwed up his mind.
A completely different story and theme can be done with The Lizard