My non-informed opinion is that this is a basic science vs invention problem.

The Wright brothers were both inventors designing an invention (an airplane) and private-sector researchers investigating the basic science of flight. Their discovery of the problem of lateral instability and its consequences for flight was a matter of basic science; for it they deserved recognition from their peers and scientific acclaim. Their invention of a method for stabilizing flight deserved a patent.

By preventing people from simply copying their solution with a patent on their method, which puts up a nice big barrier to entry to everyone except innovators such as Curtiss.