And from the BBC Sport site:
Director of BBC Sport Barbara Slater said: "BBC Sports Personality of the Year is a much-loved BBC show that is constantly evolving. Bringing in these changes allows us to celebrate even further what has been an incredible year of sport whilst also paying tribute to the achievements of individuals.
"Announcing the much-anticipated shortlist at the start of the show will add even another layer of excitement to what is set to be a thrilling night for everyone."
As has been discussed elsewhere on the forum this is arrant tosh. It is intended to restrict choice to those the BBC want and those only; no sports that they don't televise or regard as worthy of an award. If the BBC were honest about it, it might not be quite so bad, but to pretend it is for 'another layer of excitement' .... It will take at least a fire hose to extinguish your pants Barbara!