Zynga is a public company with a fiduciary duty to maximize shareholder value; but even more realistically, I'm sure Zynga executives want to get richer.
The question is not why Zynga would consider moving into online gambling; the question is, why would Zynga consider not doing it?
How is Zynga, a social gaming company in the United States, less qualified to enter United States gambling, than say, online gambling companies in Europe?
We're talking about a US customer base.
Who's going to mine that base best for mainstream users: some European poker site you've never heard of, or the #1 social gaming site--who by the way got its start with poker.