The one oddity in this Netflix + Marvel news is that Disney is a co-owner in Hulu. Going with Netflix suggests that Disney does not have faith that Hulu can be a genuine Netflix competitor, regardless of what original programming the former has.
Another possibility that comes to mind is that Disney simply wants to limit the number of parties with which it would need to share profits from these shows (presumably, the other Hulu co-owners would get a piece of the pie if Disney had gone that route).
Netflix is international, Hulu is US only. Wider distribution with Netflix.