For future reference for the people who want to stick to Steam, they will have more in due time. They just need to purchase more digital licenses with newly-generated keys before they can sell more copies to users.
As for g2a, yes, it is a very useful website as long as you are careful and pay attention to what you are doing. I personally don't like that they sometimes tack on extra charges during checkout that they don't initially show you in the cart, but it is usually still cheaper than Steam, so I put up with it.