Well, the cynical answer is their PR departments wine and dine magazine editors and journalists to write good things about them. Maybe.... but I don't think so.
To start with these are heavily branded airlines associated with football clubs, F1 racing, Tennis tournaments and other high profile cultural and sport activities. Most importantly they have what I like to call the WOW Factor;
1. New aircraft with brand new leading edge technology interiors
2. IFE systems so loaded with movies, music and games that time flies by.
3. Good point to point routes both short and especially long range that minimises multi stops
with their associated hassles of airports and airport security.
4. Good food and good service usually with a smile, consistent and enjoyable. I am not saying
they do not make mistakes but on the whole they are good.
5. And last but not least a serious commitment from the top down towards passenger service.
Not many legacy airlines can claim all the above attributes, the European carriers are starting to fray at the edges and the US carriers are so obsessed with security in the cabin that flying with some feels like being in a classroom, so uptight they sometimes forget to smile. There are the exceptional fun airlines but then most are not all Legacy Airlines.