Probably because 30 years ago there weren't as many Māori lads in the AB's, those who were in weren't as in you have with their roots as modern māori players are and so the haka as it was was a ghost impression of it.
Buck Shelford, who's Ngāphui, initiated the change in the late eighties against a background of the wider revival of Māori culture - including the first Waitangi tribunal land claims, Māori media being set up, Māori immersion schools, reinstatement of traditional roles within Māori society etc.
By the early 70's it was reckoned Māori culture was almost dead, a result of a govt that tried to stamp it out in the early 20th century (writing in Te Reo was illegal, kids were beaten at school for not speaking English
).
After Aaron Smith got caught in the toilet with a woman who wasn't his partner last year, he got stripped of leading the haka because he didn't have the mana to do it any more. It would have been disrespectful to the culture for him to lead it. More going on with this than you reckon
Far from it becoming 'sinister', it's becoming more accurate. The video you can see showing the development of it over the years, from an awkward half arse set of motions to the proper stuff you see today is a great marker of the regrowth of māori culture in Aotearoa
A good haka, done well, is a beautiful thing
They could do without the SFX guys giving it the fire mind