Good question, Timothy. For a long time I have wondered about the same thing. I sort my aircraft photos by make, model and further breakdowns-Warbirds with further sub groups, Experimental class aircraft with further subgroups, Production aircraft with further breakdowns, S/LSAs, Military aircraft, Helicopters, Lighter than air, etc. etc. As I had so many floatplane photos, I put those taken at LHD under a sub-heading of the world's largest seaplane base, a deviation from my usual approach.
There are far more aircraft photos than airport photos on this site. Someone wanting to find a particular photo or photos of aircraft by make and model would be hard pressed to find them by looking in the Airports section of any contributor, I believe. Search Aircraft feature here brings up an aircraft photo, but not one filed by airport code in the Airport section
In Europe and in the U.K. there is far less General Aviation flying and it is heavily controlled for between country flights. Is the U.K. still charging pilots for every takeoff and every landing at a U.K. airport? Practically all the German exchange engineers from Germany who worked at Point Mugu in technology transfer tours learned to fly in America in Point Mugu's Aero Club, first based at OXR and then at NTD, as we had so many aircraft in the club and they were so inexpensive to fly, even our T-34 warbird, as compared to learning in Germany. Many European recreational pilots get the glider rating only as that is much cheaper. Further, are more of the European contributor photographers non-pilots, hence less air to air aircraft shots?
I average one request per week for use of one or more of my aircraft photos. Far more rare, for example, I recently got a request from an FAA Safety Officer in Anchorage, Alaska for use of a Merrill Field Tower airport photo of mine in preparing his presentation to local pilots. I'm also a North American.