It's a nice thought. Who knows the reason why, though?

[To be honest, he's kind of making this up as he goes along. The Creators gave them an incomplete understanding of the human body, a small but hugely important hole in their knowledge. He clearly remembers Ergo Proxy's/Proxy One's despair at not being able to make humans complete, but he can't guess the reason why the Creators included sex in the blueprints despite not including procreation.]