This was another new thing to me. Steam accounts, which are essentially free can be worth money. Apparently low four and five digit accounts are in demands and sell for hundreds of dollars.
Why? Well, the “coolness” factor is a big part but there’s more to it as well. From what I gather having an older account creates the perceptions that you are a long time and hence good, player. For those that like to hack this lowers the chance that other players flag them as such.