There can be lots of legitimate reasons, such as the material a frame its made of, its brand (a BD brand is resale suicide as opposed to say bianchi), its condition (if it was stored outside at the mercy of the elements as opposed to a nice and dry and dark garage; "new years resolutions bikes"; owned by a bike mechanic/ professional), its rarity, its place on a bike maker's model hierarchy, etc...

There are also illegitimate reasons which would be a person trying to milk CL for profit, take advantage of the fixie hype for profit, etc....