Humans were favored by the Father above all others. Azazel has always been curious. He no longer remembers the name or face of the man he took as a vessel, nor of the woman who mated with that man. He never knew the names or faces of the vessels of Ramael or of Shemhazai, or of any of the others curious enough to follow him.
Food, dreams, sex; these aspects of wearing mortal flesh were appealing, but the limitations of mortal flesh were such that Azazel never did understand why Father liked humans so. Children were little squalling things that caused far more trouble than they were worth and couldn't be understood or made to understand, though his own children could at least hear his voice when he wasn't speaking through his vessel's lips, could see as he did when he didn't use his vessel's eyes, had all the senses and abilities of angels though weakened by their unbreakable ties to mortal flesh.
When Azazel's grace was torn from him, for the crime of fathering half-angel children, he swore eternal vengeance on every human born. When Azazel's grace was restored, even if it was a fraction of an archangel's grace instead of anything of or as strong as Azazel's own, he swore eternal loyalty to that archangel.
Later, long after Lucifer finally gave up on God and humans both and shattered a human soul into another sort of demon with a fig and a drop of grace, long after Lucifer was locked away for what he had done to and for Azazel and Lilith, when Azazel heard Lucifer's voice for the first time almost since Lucifer had gifted him grace, when Lucifer asked Azazel to find him a special child, it was the descendants of Azazel's half-human children whom Azazel sought out.
(Were it possible to trace genealogy back to before the first humans set foot outside of Africa, one of Deanna Connell's many-greats-grandmother is the first daughter of Azazel. John Winchester is descended on his father's side from the third daughter of Shemhazai; on his mother's, from the second son of Ramael. The descendants of Ramael and Shemhazai number few enough that in all the world, only John and his sons have the blood of both.)