Because let's face it, when the All Blacks perform the haka not many people even think about its origins.
"Many of the general public don't know where it came from and the time when it originated. So knowing that the World Cup was coming up, and that there would be a lot of interest in telling the story, I thought it was a good time to get a documentary up and running," says Grace.
He had wanted to tell the real story behind Ka Mate for a long time. His original plan was to make a short film. However, it evolved into a film that cleverly mixes dramatisation and documentary, historical footage, and interviews with everyone from kaumatua to All Blacks such as haka leaders Norm Hewitt and Buck Shelford, as well as blokes like English hooker Richard Cockerill who famously had a set to with Hewitt before a 1997 test match at Old Trafford. "It was like two bald-headed pitbulls, face to face, nose to nose, full on, and no one took a backwards step," remembers Hewitt.
The spectacle Ka Mate has become in rugby circles is a far cry from the time of violent warring 200 years ago when the haka came to be.
The story - albeit the short version - goes that Te Rauparaha was being chased from Kawhia by members of Ngati Maniapoto and Waikato tribes and he sought refuge at the pa of Te Wharerangi at Lake Rotoaira in Tuwharetoa and Ngati Hikairo territory. Although reluctant to shelter Te Rauparaha, Te Wharerangi hid him in a kumara pit, throwing his pursuers off the scent - and when he emerged he performed Ka Mate.
The dramatisation of this chase scene is thrilling, like Utu only darker and more mystical, with portrayals of cannibalism, ruthless warriors, and best of all, the sinister and scary tohunga (described beautifully as "spiritual bloodhounds" in the film) who try to see inside the mind of Te Rauparaha.
The majority of the dramatic footage was filmed around Lake Rotoaira which, says Grace, meant the film tells the Tuwharetoa and Ngati Hikairo side of the story too.
"They were the ones who protected our ancestor, after all," he says.
Despite Ka Mate covering many time periods, and incorporating many different voices, Grace keeps it focused by telling the story of the haka from Ngati Toa's point of view.
"I built from there. I basically wanted to tell a story that was as authentic as possible in terms of the drama, and authentic in terms of the story of Ngati Toa and how we have struggled with adversity."
Following Te Rauparaha's death in 1849 it was his legendary status as a leader, warrior, and survivor that kept the haka alive for 50 years until it was picked up again - and mainstreamed, as Grace puts it in the film - following a performance by politician Sir James Carroll in 1901 during a Royal Tour by the Duke of York.
And then it was adopted by the 1905 Originals All Blacks team. Initially though, rather than a challenge to the other team, the All Blacks performed Ka Mate for the crowd as pre-match entertainment. Fast-forward a few decades to the 70s when commentator Keith Quinn remembers the team doing a "pakeha version" of Ka Mate ("It wasn't very vigorous").
It was during Buck Shelford's reign in the 80s that the All Blacks started doing the haka properly. Shelford: "I said, 'Unless we're going to do it properly we just don't go near it'. [Because] those Pakeha boys didn't have much rhythm, eh?"
Although, judging by the old footage, even under Buck's tutelage John Kirwan still struggled keeping his flailing, wayward arms under control.
For Shelford, Te Rauparaha's words still ring true today: "For a sportsperson who is going out on to a field it's all about winning and losing. And when you lose, okay, it's not death but it feels like it."
While Grace appreciates the profile the All Blacks have given the haka, he still believes Ka Mate's rightful place is being performed at a tangi or on the marae.
"I'm not precious, and don't mind the different ways people do the haka. But the important thing is that people know where it comes from, know its origins and respect that."
Lowdown
What: Ka Mate: The Haka The Legend, the story of the haka
Where & when: Saturday, October 1, 8pm, Maori TV