The Chitauri weren't completely wiped out in Avengers as we see one member of the Chitauri still alive in The Collector's collection in Guardians of the Galaxy.
As such we can assume that the nuke blast in Avengers only killed those being controlled by the mothership that it blew up and not the entire army.
We also know of The Other, the Chitauri leader, who survived up until some point in Guardians of the Galaxy when Ronan kills him. This backs up the theory that again not all of the Chitauri were killed.
Click to enlarge.
A deleted scene from Avengers: Infinity War also shows a member of the Chitauri working on Nebula and guarding her before she escapes. This is non-canon (as it was changed for the film) but shows that the film's creators might have believed them to have survived.