Underneath it all is the same operating model that allowed low cost carriers to flourish in the short-haul market: streamlined, standardized, modern, fuel efficient fleet; non-unionised crews; using cheaper secondary airports; flying direct; cramming in as many rotations in 24 hours as possible and flying outside of peak hours to get cheaper landing slots.
The new Boeing and Airbus models make the LCC approach increasingly viable for longer haul routes thanks to big fuel efficiency improvements and smarter cabin interiors/materials that boost pax load without sacrificing comfort. Oil prices are also helping since the price has remained low for so long now that even if an airline hedged the wrong way a few years ago they're now all enjoying better rates.
IAG (British Airways, Iberia) and Lufthansa are trying to get in on the action too with Level and Eurowings respectively.