They didn't set out to create something new and wonderful, they wanted the operating system that they loved to have a life after Be. Recreating that OS was a design goal, because if they had decided to create something new and different then they would have had to sit down and figure out what exactly that means and nothing would have ever gotten done.

Haiku has always been about recreating R5, just a bit more modern, because it's a goal everyone can agree on and no major design work was necessary.