In addition to what has been said already, in many places the cost to upgrade the electrical service to the building to handle the amount of power that could be generated can be as much or more than all the other costs combined. So now the building operators are looking at millions in cost with a potentially 30 year payback period. It just doesn’t make sense at that point.
Shooting two guns at the same time does in fact look cool. That’s not a myth. Hitting two targets with two guns at the same time is really hard though.