Sorry, but it does make sense. They have publically disclosed to analysts that they are selling older 737-800s (see earlier post of mine, cited from Chris Avery of JPMorgan).
Like they have been doing since the past decade. Any aircraft older than 5 years is sold because it would cost too much to maintain it.
Explain how they would otherwise achieve an average fleet age of 2.5 years.
Ryanair are doing great.
And so are most European airlines not flying regularily across the pond.