The desire for lightness, maneuverability and higher speeds was the basis for the bobber and cafe racer style
While bobber was a customizing style of the 40's and 50's in the USA, the cafe racer didn't appear until the 60's in England. Classic bobbers were based on the board track racers and hill climbers of the time. Mostly thick balloon tires of the same size, the front fender was mounted to the rear, which usually created the "bob", the small outward curve that old Harleys had at the lower end of the fender. All in all, everything that wasn't necessary was eliminated in favor of a lower weight and improved the then turgid and cumbersome appearance.
Cafe racers were created as sporty conversions of English production motorcycles, also reduced to essential parts with flat clip-on handlebars, an open exhaust pipe and a shortened, sloping seat. The name comes from the street races of the British rockers of the time, which took place in particular at the Ace Cafe. Loud and fast, the cafe racers were an important symbol of the young rebels' rebellion against establishment norms of the time.
Of course, both styles had an influence not only on the motorcycle but also on the clothing industry. While the English rebels were characterized by heavy leather jackets, which they also wore for their races for protection, the bobber drivers were more careless, sometimes only wearing striped shirts, analogous to the board track racers.
No matter what style you ride today, and whether it's a standard machine or a custom one, both have one thing in common:
Reduce everything to the essentials. Only do what really counts.