Most advanced visual programming systems I'm familiar with can't be properly read or manupulated by anyone except even tinier minority of people who specialize on working with the particular system.
And a diagram (in such a 4GL) does not help when it has hundreds of decision nodes and the end-user (read: a human being) visual system can only deal with at most 10 nodes.
It is also very amusing when the executives finally realize how unnecessarily complex their order processing chain is.