Board Thread:General Discussion/@comment-26643527-20160328025333/@comment-25926288-20160328025810

It could happen as Hades' isn't technically the God of Death, but the Dead. Thanatos has that honor.

I think they skipped ahead to Disney for marketing purposes, plus, it was a decent business move that may not have been that successful. (i.e. they cashed in on the Frozen Hype to give a boost in ratings which then balanced out the really low rating of season 4b.)