The system for choosing arena settings is broken (for all games, not just Azul). Because those who play the most games choose the settings the games tend to be played by those who like the current settings, and everything stays the same.
In most games low player counts play faster. And so those playing the most games tend to play with low player counts. And so arena settings tend towards low player counts, even when that is a poor choice for the game.
As it happens, in Azul 2 player is the most competitive way to play it. But it Catan 4 player is the most competitive way to play (all face to face tournaments are four player including international tournaments) but the gurus keep it at 3 player.
BGA needs a much more open way of creating arena settings and abolish this guru nonsense.