Loki, Asgard's former second prince and current Eldest Princess, was a certified scammer who somehow always managed to fool people.
It was hard to imagine anyone getting fooled by someone called the God of Trickery. She had practically written "I scam people" into her name, yet there were still people who fell for it.
Perhaps this was how Loki screened her target clientele. Anyone who still welcomed her after hearing her title and record was usually a wealthy, gullible fool, and the Chitauri were no exception.
The Chitauri were a very peculiar civilization. Their planet's orbit was unstable, and their homeworld remained frozen year-round. Yet they were also extremely violent, fond of capturing people from other planets and throwing them into the gladiatorial arenas on their world.
After those gladiators were killed, their spurting blood instantly froze in midair. The Chitauri would then pluck down those crimson snowflakes and feed them to their children, cultivating an extremely warlike, cruel, and bloodthirsty temperament.
The Chitauri Empire was not a civilization that had developed entirely on its own. Their technological explosion began when a more advanced spacecraft crashed onto their homeworld. After reverse-engineering much of its technology, they stole ships from many other civilizations, pieced them together into vessels of their own, and eventually built Will-class battleships.
However, the strongest flagship among the Will-class battleships, the Leviathan, had actually been modified from a miraculous creature known as the Space Shark.
In other words, Loki tricking the Chitauri into coming to Earth to fill this bottomless pit was, in a sense, thieves robbing thieves, because the Chitauri themselves were famous thieves and swindlers throughout the cosmos.
Loki's original plan had been sound. The Chitauri's own battleships had been cobbled together from countless sources, and much of their stitched-together technology would be highly useful