So, as he told The Hollywood Reporter, Zak Penn focused more on the other characters in the beginning, playing down the more comic book-y character.
This seems so silly now but when Zak Penn was initially brought on to write The Avengers, the MCU was in its nascent stages and Thor had not yet proven himself on the big screen.
Simply having Loki as the villain necessitates Thor’s presence as a protagonist and someone to explain the cosmic side of things.
The idea of audiences buying a long-haired, hammer-wielding superhero who also happened to be a Norse God and an alien must have been laughable.