A lot of it is because people who have been playing for a while fill up their inventory slots and use the bazaar to hold items they'll use later(Mats for crafters, arrows for archers, etc.). And probably sometimes it's just to be silly.
In some cases it could be showing off something nice. A way to say "You will never get this, you will never get this!" = D Or perhaps they might sell it if given a great offer.
Yea, that can be annoying for a new player expecting to see stuff actually for sale when checking all those bazaars. Would be nice if you could put up another icon with it that says "I'm not really selling the stuff in here, it's just storage". Because a ton of people do that...
Edited, Apr 1st 2011 2:48am by TwistedOwl