I truly hate what Oda did to Kaido. I guess he figured he would be unbeatable if he was Awakened. Still, no excuse for fucking Kaku to be awakened and not Kaido.
Awakening happens when your mind catches up to your body. Meaning that your mentality matches your DF ability.
Luffy is awakened because he's pure-hearted and free-spirited like Nika.
Doffy is awakened because he is an expert manipulator, which matches up with his string ability
Law is awakened because his surgical skills match up with his operation DF ability
Lucci is awakened because he's like an apex predator.
Kaido didn't awaken because he isn't like an eastern dragon, which are supposed to be benevolent deities
WB also didn't awaken because the destructive capabilities of his fruit doesn't align with his desire to protect his family