Considering how integral the story is to getting into Ishgard and the lack of Ishgardian presence throughout the ordeals against the primals, Garleans, and operation Archon up until Shiva shows up, it makes perfect sense to gate it behind story.

Sucks for people who want to start off as DRK/AST/MCH and those who care little for story content, but that's how it is. Tough cookies.