The sheer number of people selling bikes with virtually no mileage on them is amazing isn't it?
There are probably as many reasons as there are bikes being sold, so there is no single answer.
Some people decide that they need a faster bike, some people decide that they don't need the same bike Lance rode, some decide they need a more upright position, some decide they need a more aggressive position, some had someone giggle at them for riding a substandard bike, some had someone giggle at them because they paid $5,000 for a bike, some had their significant other withhold sexual favors for daring to spend $2,500 on yet another bike, some thought that a $3,000 bike would make them fly up hills and discvovered that it still takes work, just like on their 2007 $2,000 bike that is just fine.
Some just have other things happen in their lives that make them need the money for other things. Like home heating oil hitting $4 per gallon, or have a baby on the way, or have to buy a car to replace one that won't run any more.
Some stole a bike that they want to unload.
Some have decided that the bike is the wrong color.
Well, if u frequent here enuff, u'd notice an alarming number of ppl willing to open their wallets by a single post of somebody they don't know saying they like bike xxx. Ppl buying their bikes then ask basic questions that they should had answered b4r the purchase.
Ppl "fall in love" then realize they have to ride the dang thing and sweat and spills and safety and pretty soon they've fallen out of love with the whole thang.
I have a friend who once bought a brand new Oldsmobile sedan and within a week or 2 decided he would rather have the next model up in a different color and traded the car back to the same dealer. He lost over $5,000 on the trade for the same model year car. This was way back when 5 G's was real money. No different with anything else.