Nobody Chose BSUF. You Just Followed the Path of Least Resistance.
Big Spec Up Front failed. Not because the people who practiced it were careless — many of them were meticulous. It failed because of something structural: the act of implementation always reveals things that specification missed. Users cannot fully articulate what they want before they see it. Complexity defeats even complete knowledge. External requirements shift before the system ships. Agile was the response. Short loops. Working software over comprehensive documentation. Iterate toward understanding instead of specifying toward it. ...