For show. Self esteem. Some people just like to start discussions. What you think something is worth and what someone else does does not matter.
If I buy something it is because it is something I want and the selling price is in my buying range.
Those threads are really no different that. "Player X is the best in the league"
100 people and you will have 73 different responses.
Thin skinned megalomaniacs shouldn't post on message boards.