Because Hook is a series regular and there are still a lot of uncertainties about his backstory. For instance, we have yet to see the story he told Baelfire about his father. We don’t even know which kingdom Killian Jones and his brother came from. We also know next to nothing about his years as a pirate prior to or after meeting Milha.
David and Emma are both series regulars/leads and we where told this Season we would learn more about them. There is a lot we don’t know about David too.
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