It's worth underlining just how hard the American carriers have been fighting against Norwegian and WOW under every excuse they can think of: "unfair" competition, spurious safety concerns, labor laws, strong-arming airports into denying them landing spots, etc. My favorite example of chutzpah was claiming that lower fares are "not in the public interest" (...because what's good for AA is good for America, right?).
In general, international flights to the US remain remarkably restricted and regulated. Foreign carriers aren't allowed to transport passengers within the country, transit without a visa is completely impossible, etc. Compare this to the EU and (soon) even South-East Asia, where anybody can fly anywhere they wish, as long as they fulfill standard safety requirements.
http://time.com/money/2827588/cheap-flights-europe-norwegian...
In general, international flights to the US remain remarkably restricted and regulated. Foreign carriers aren't allowed to transport passengers within the country, transit without a visa is completely impossible, etc. Compare this to the EU and (soon) even South-East Asia, where anybody can fly anywhere they wish, as long as they fulfill standard safety requirements.