Pat, I doubt if you'll get any answers to your question. Instead I'll pose another question.
How many chemical manufacturers would register one of their products for an obviously efficacious type of treatment, IF knowingly endorsing such treatments might pose a chronic health-liability to the manufacturer? Think asbestos...
Ultimately, (IMO) this is probably why DuPont never pursued an EPA registration for diuron's use in aquatics; and they certainly aren't obligated to explain their decision.
Interestingly, diuron "was" registered in Canada (circa 2006) - albeit briefly - but the label lists very specific exclusions. See below.
