Why are current Greek names long and complicated compared to those we see in ancient history and mythology?

See also Dimitra Triantafyllidou’s answer, which this is complementary to.

First names in Greece are either (mostly revived) Ancient names, Judaeo-Christian names, or Saints’ names (which end up being either of the first two). There are a few later names (though they are less in vogue now), and some of them can be long, like Triantafyllos ‘Rose’; but as Dimitra says, the names that seem long and complicated are the surnames.

The reason why surnames seem longer is that:

• They almost always include a patronymic suffix: -opoulos, -akis, -ellis, -ides, -atos, -oglou, etc.
• They often include a prefix: papa-, kara-, hatzi-, deli- etc.
• They are based on the ancient/archaic form of proper names, where applicable, which adds syllables. John is Yannis in the vernacular, but surnames will always add two syllables by basing it on Ioann-: Ioannidou, Papaioannou, etc.

So Papahatzidimitrakopoulos is a comical exaggeration for surname length, but not by much: both Papadimitrakopoulos and Hatzidimitrakopoulos are real surnames.