Atheists concentrate on the supernatural aspects of religion because we know that ripping out the floorboard of supernaturalism destroys religion. The building can’t hold without that board. If the supernatural component is removed from belief, you have no belief. It really is that simple.
Communal solidarity is great and necessary and important. But why do people feel a need to overlay this solidarity with supernatural nonsense? Why can’t people just be utterly and totally secular with their communal get-togethers? Sorry, I forgot. Such opportunities do exist. They’re called The Arts. But attendance has always been low. Go figure.