For one, there’s tons of competition on transatlantic routes. Not only from ultra low cost carriers, but the reality is that nowadays even legacy airlines have incredibly low transatlantic fares, because they know they have to compete. $400-500 roundtrip fares on major carriers are the norm in the off season.
When fares are that low, it really makes you wonder what the point is of flying an airline like WOW Air. Even if they charged $200 roundtrip (which is way lower than their usual fares), you’d end up paying more by the time you paid for baggage, food, drinks, seat assignments, etc.
How are other airlines able to charge these fares? Because the major airlines aren’t making money off economy transatlantic fares in the off season. Think of those cheap fares as paying a bit of gas money, but the reality is that airlines make their money off the handful of people on each flight who are spending $10,000 for a full fare business class ticket. That’s where the money is, and the rest is only working towards breaking even. Ultra low cost carriers don’t have those lucrative passengers.
Source: Why Did WOW Air Fail?