Well, having worked with various 4GLs that were meant to improve productivity and produce re-usable code, ones that are being used merely add more accidental complexity rather than reduce it.

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.