It's a matter of timing. You can't make any money on a film in the US when all three major theater chains pull out. The revenue that's left from the small operators probably isn't enough to cover distribution and marketing costs.
On CNN, Sony's CEO said they really want to show the film, and I don't doubt that they do. But it's a business, so the business calculation is basically that they've got to show it at the right time and in the right media (screen, streaming, DVD, etc.) to maximize their audience and revenue. The original date of December 25 that has been threatened isn't the right time, now that the theater chains have pulled out, but the right time will come, maybe soon. In any event, at least a few of the North Korean people will get to see it when DVDs eventually get sent to them via balloon. Hopefully, it isn't as bad of a movie as the reviewers (and the trailer) suggest. Those poor folks deserve some quality entertainment.