Six-digit ICQ is fashionable?

"Hackers" steal short numbers ICQ, it brings inconvenience to users and brings some income "hackers." Everything is clear, but it’s not at all clear who buys these numbers and why? After all, the number is used only before communication, and then everyone is guided by nickname or name. Especially if a person is 15–20 years old, then he is unlikely to have a six-digit ICQ received by himself.
Do you know the motivation of those who create demand for short numbers?