"Chalmers argues that since such zombies are conceivable to us, they must therefore be logically possible. Since they are logically possible, then qualia and sentience are not fully explained by physical properties alone."

This is shorthand for "in the two decades that Chalmers has been working on this problem, he has been defending the argument that..." You might look at his arguments and find them lacking, but he has spent much longer than five minutes on the problem.