From past experience the issue was what else you might have in your photo in addition to any aeroplane. It used to be a concern that you might have Customs staff or security staff in the photos, and they for good reason do not wish to be photographed.
These days I imagine that there is a wish to deny those who are not well meaning from being able to photograph security sensitive parts of the operation under the guise of taking a photo of the aeroplane you have just flown on.
It isn't a new issue. Back in the 1980's I worked airside and had to get a letter from the Airport Authorities to allow me to take photos airside. It was made very clear what I could and could not take photos of, and also that they could not be sold on for commercial gain.