Possible "old wives tale". Pierce-Arrow received a patent on "headlights integrated into fenders" in 1913. After that, most of their cars used this feature. Other American cars didn't follow until 1937 or 1938, when Pierce-Arrow was fading away or gone. Many European cars featured headlights integrated into fenders, before 1937.
It may be, that most car makers didn't see the need for the design, or thought the public wouldn't like it. I haven't been able to find information about Pierce-Arrow licensing their headlight design to others, or enforcing it.