After World War II, countless veterans came back to America and many of them had a difficult time readjusting to civilian life. They searched for the adventure and adrenaline rush associated with life at war that had now left them. Civilian life felt too monotonous for some men who also craved feelings of excitement and danger.[3] Others sought the close bonds and camaraderie found between men in the army.[6] Furthermore, certain men wanted to combat their horrifying war memories and experiences that haunted them, many in the form of post-traumatic stress disorder.[7] Thus, motorcycling emerged stronger than ever as a substitute for wartime experiences such as adventure, excitement, danger and camaraderie.[3] Men who had been a part of the motorcycling world before the war were now joined by thousands of new members. The popularity of motorcycling grew dramatically after World War II because of the effects of the war on veterans.
https://en.wikipedia.org/wiki/Hollister_riot#Rise_of_motorcycles_after_World_War_II
I'd rather be a forest than a street