I have NO idea. I can blame editorial for a large portion of this -- they don't treat Namor or Atlantis like the substantial part of the MU it was and should be. But a portion definitely belongs on the creators. But IF you are setting up your book with a freaking Atlantean mystery / plot, WHY would you wait??? It's not like Marvel has a long run on a typical superhero book in a decade. And this has happened repeatedly. Fraction, Yost, Hickman, Robinson, Robinson, etc.
That's why I give Zdarsky big kudos, even if I didn't agree with everything he did, because Zdarsky didn't yank us around. He went straight to the Namor plot. THANK YOU.
And yes, I'd even settle for a GOOD Namor animated show. That would at least prod the comic side into giving Namor a book.