Someone wants to sell something, they go on CL looking for the price of similar item. They find said item for stupidly high price (hence it still being on CL). They think that is the price they can get, so they ask for that price. Their item stays there for months, strengthening the cycle as now there are several items listed at ridiculous prices.

Whenever I see a good deal on CL, it disappears in 1-2 days. Others stay there forever.