I don't know why. And given enough decades, it may appreciate. As it is, if someone had bought Georges for IIRC 120k+tax in ~2005, that would be about $205K in 2024 dollars. This bike is listed at $95K (plus tax but we know that is flexible on a private sale). If you put the 205K into S&P500, you would be at about $1.2M now. It will never appreciate enough to make up the lost opportunity cost of recent times. Now, is it a good investment at 95K in 2024? I suspect not but time will tell. It is really pretty.
EDIT:
I obviously got the year wrong as it was only 2007-2008. Finances aren't quite as bad as I listed above but still crap. I can't be bothered to recalculate.