Winston Royce wrote an article describing what he saw in the US DoD which became the kernal of the waterfall software development process.
As Glen will tell you, the DoD has moved on and has gotten smarter. It takes some organisations a while longer to catch up. Especially while there are vendors out there peddling material hat steers you in the wrong directions.
Where did your organsation's project and software delivery methods come from?
Just like with detective stories and requirements analysis, my advice is: follow the money.