If you read the Financial Times report, the talks were held in secret in January, and quickly broke down as the US would only offer a standard bilateral agreement. The killer clause to that is that it requires airlines to be majority owned and controlled by parties from their country of origin. Under EU-US open skies that means EU owned (I assume Norway are included in this) airlines can operate anywhere in the US. However with Virgin being substantially owned by Delta and Air France; BA being an IAG subsidiary, and Norwegian being, well Norwegian there lies the problem.
A graphic illustration that the bigger the imbalance between partners, the more likely the smaller partner loses out. Unlikely to be the only example over the next year or so.