Am Going To Say This One More Time
States were being leaned upon by the federal government via the Clean Water Act to get their acts together regarding water pollution. In many cases they could have been forced to build new and or upgrade existing water treatment plants. Feds also want things done to tackle water run-off from lawns and so forth.
Much phosphate can be recovered/removed from waste water, indeed as human waste contains tons of the stuff. However if one adds amounts from dishwashers and other sources it can quickly overwhelm many older systems. When states banned phosphates in domestic laundry products, automatic dishwashers weren't nearly as common as today. Of course today most every home has one.
NYC and other areas of the state were staring down potential scores of millions if not hundreds if forced to build new plants. Funds they nor many other local areas have right now considering the current fiscal meltdown nationwide.
Eaiser answer was to limit what goes into waste water, which is why NYS moved not only to ban phosphates in domestic dishwasher products, but commercial versions as well. Furthermore restrictions were placed on lawn care chemicals as well.
The EPA isn't finished, despite loud protests, sooner or later farm waste is going to be addressed.