In my experience there are a few serial bike swappers who really don’t care, a shiny new rig every 6 months makes them happy and fair play to them, better that than coke and hookers.
However the majority of these nearly new bikes popping up tend to be incidents where the household finances have faced an expected squeeze:
“Darling I’m pregnant”
“I want a divorce”
“The Car’s crapped itself”
“You’re fired!”
etc etc
And in these instances swanky bikes are high value, non-essential and easy to sell so they tend to be first in the firing line if you need a bit of quick cash to cover the mortgage for a few months whilst you sort things out. Better that than pay-day loan vampires.
The obvious alternative of sticking your kids on Ebay in the hope Madonna or Angelina Jolie will stick a bid on them also tends to be frowned upon by society in general.