The large number of empty seats notwithstanding, had you arrived at the gate earlier you probably would have heard the GA announcing "Ladies and Gentlemen, this is a completely full flight, so we are going to ask those with rollaboards to....etc."

Not taking a shot at the GAs or FAs... I just hear this in far too many situations that turn out similar to yours.

I am starting to believe it is a spiel that they are required to say.