Opening on Xmas requires a movie to have legs.
Franchise movies, traditionally, don't have good box office legs (doesn't apply to LOTR). They are front loaded, as this movie will be, and then fall hard.
Given the nature of this movie, and the lack of mainstream interest in Star Trek, an xmas release is horrible. But Paramount has been making blunders left and right so why should this be any different.
Star Trek is NOT a family movie. It's going to face fierce competition and flop.
The biggest xmas day opening, of all time, is Ali at 10 million. That is not really that great. Nowdays blockbusters have opening days of 30+ million. It's a busy day for theatres but that business is spread for all the movies. Studios don't waste hit movies on xmas they open them a week or two before and then get an xmas bounce. That is exactly what fox is doing with The Day the Earth Stood Still, which will completely destroy Abrams Trek.
Paramount NEEDS this movie to perform like a summer blockbuster. They needed the summer hype so they could get a massive opening weekend.