Simple: to kill the negotiations. They never planned on the negotiations working out. They needed a way out. In the past, whenever negotiations were working out, the US imposed the demand that Iran abandon enrichment, knowing it would kill any deal. That's what they did with the Brazil/Turkish deal.
This time, they again announced that they would not recognize an enrichment right in Iran and are now using France's objections as a way to back out yet again when they saw they couldnt intimidate Iran into abandoning her unquestionable and absolute rights. That's all.
How many times will we have to watch reruns?
I don't know how many times I have to say it over and over again: they have no intention of making any kind of actual deal with Iran that respect's Iran's rights.