Elinor: You kill people for money?!
Apollo: I can explain!
Elinor: And all this time I’ve been doing it for free like a chump!
I don’t know if this is already been stated but I think the only way to turn someone in First Kill is if they are dying. In First Date, Sebastian stated that Margot changed him when he got really sick. Sebastian was again sick before he got turned into a ghoul/vampire by Margot’s mom. Theo was turned when he was about to die by Juliette. This could be the reason why Cal and Cook didn’t turn.
Just a thought though.
Juliette: What’s up guys. I’m back.
Calliope: What the- you can’t be here. I literally saw you die.
Juliette: Death is a social construct.