Why NO FUN at work?

This is a serious question and I'd really like to engage you in considering answers. I have done a little research - and I admit to not being especially skilled - to find publications that can explicate and enumerate reasons for no fun at work. And I haven't found very much.

Here are some of the reasons that I have seen articulated:

• There is no time for fun. 
• Fun is counterproductrive (if not unproductive). 
• Business is serious. It is not professional to have fun. 
• Fun is disruptive. 
• There is a workplace, not a play ground; there is a workforce not a play force.
• Fun requires people to participate whether they want to or not.
• Fun carries the risk of offense to colleagues.

There are probably other reasons and rationales. One that comes to mind is that leadership is not comfortable with the idea of fun at work. 

So help me out, please. Why is fun at work such a hard sell?