My guess is this. It is new. It got created because Spring Roo was using Tiles. And so they created Surf to work with Tiles in a Roo app. When I used Roo, one of the things that I didn't like was that it used Tiles. I prefer xhtml files with templating that way, it is much cleaner and you can't abuse it as easily as you can with Tiles.
Since it is new, there isn't a lot of people yet using it or aware of it. As more people use Roo more people will be aware of Surf.