Except if they weren't so much of the corporate mindset they'd grasp that digital is so popular now that a film image winning is no threat to their business.
What really gets me is, they allow images from formats in which they have never even made cameras (lenses, but not cameras) so the contest is ostensibly open to all, but it must be digital when the cost of those formats in digital is prohibitive to most people. If they are going to allow large format, they should allow all using that format, not a select well-heeled few.
They don't want to be shown up by film, but they will be hurt far more if the winning image comes from a Canon.
I'm certain that it's not the photography types at Nikon who are doing this- it's the soulless corporate suits who claim that their business is "business", and see no reason to truly understand or even respect the business for which they work. I've seen a lot of them in my time, and there are more now than ever.