When I started riding motorbikes in the UK of the seventies ,I suppose we were hairy bikers .Certainly if you walked into a pub or restaurant wearing a leather or a Barbour jacket you were very likely to get thrown out before you could utter a word .
We were seen, I guess ,as a subculture ,the evil children of society .A tag that was hung on us because of the antics of the Rockers during the sixties .

We weren't acknowledged by society ,so it was normal to acknowledge one another on the road by a nod or a wave .Bikes were owned by cash strapped enthusiastic kids [like me] , "Ride to work Ronnies" on commuter bikes who didn't really count as bikers and -those guys we all envied - ,the experienced tradesman who rode bikes out of choice and had the latest and best machines .

Time passes and bikes are now usually the second or third vehicle in the household .Bike owners are less enthusiastic and ride in the summer instead of all year round .The social barriers are less visible these days and many bike riders do not really know much about the bikes they ride.
There used to be only "standard " bikes available , if you wanted a cafe racer or a chopper you had to make it yourself .Now you can buy just about any kind of bike you can imagine with zero input from the owner other than providing the cash .So the individual involvement is less .
Cafe racers used to be my cup of tea but I'd always wave or flash my lights to chopper riders ,not only to acknowledge them as fellow riders but aslo the input and effort they put into their machines .
Cameraderie I guess .

Motorcycling is fragmented because of the specialised bikes and the riders they attract .The commitment to bikes is less because the only input is cash ,when cash is short the bike will go before the car .
That's why they don't wave ,they don't see themselves as motorcyclists .

Wave to the buggers ! [and shake your head when they don't wave back ]

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Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."