Southwest is not really the equivalent of Ryan. Spirit airlines has plenty of $22.22 flights (for two's-day, I guess), glancing at their page today. This includes e.g. Chicago to Tampa, Texas to NJ, and other flights longer than most European flights.
They look very much in the style of Ryanair with the garish website. $22 for three hours (Boston-Miami) is priced between the two Ryanair flights, so I expect the "service" is similar.
I'm sure the average distance of a flight within Europe is lower than in the USA, since the USA is a bit empty in the middle and Europe has more water in the way, but routes like Scandinavia to the Mediterranean (Stockholm to Zagreb is 3½ hours and $14), or Britain to eastern Europe (London - Cluj, 3 hours $13) aren't far off, and the budget airlines also have flights to tourist destinations in Egypt, Israel, Jordan etc, which are as long as a US coast-to-coast flight.
I’ve been on a flight between Berlin and London that cost less than an Amtrak return ticket from Davis to Sacramento, and I’ve also been on a multi-day road trip from Davis to Salt Lake City that, while fun, was only a good financial choice due to four people squeezing into a Prius.
While I enjoyed camping and seeing bits of the US that foreigners like me don’t normally see, it’s not entirely clear that the difference between that and flying makes flying the luxury.
In general flying is more expensive in NA because of less competition and bigger distances. That's what I noticed when I moved from Europe to here. Now you have to take expensive tests to fly international both ways. That's why I consider it a luxury.
Downvotes because you seem to think there is something special about flying in Europe? lol. It is a similar size to the US within a reasonable estimation, let alone the whole of NA, which is probably what 3x as big?
Edit: why the downvotes? You can get flights for 50 bucks to go to different countries in Europe.