I’ll throw in my pet theory. American football is rooted in infantry maneuvers Civil War through WWII. Soccer is closer to cavalry, a Second Millennium European experience.

Cavalry was never that important in the military experiences of Americans since its founding a mere 250 years ago, whereas lots of folks served in the infantry — Civil War through WWII. The US, moreover, is essentially a 20th Century country; infantry, tanks, air forces, etc. is 20th Century warfare; and American football echoes those 20th Century technologies.

The romantic ideal and practical effectiveness of cavalry over many centuries, ending in the 20th Century/WWI, made it much more deeply ingrained in the European (Old World) psyche. Soccer is cavalry, thus Europe and past colonies gravitated towards it.