Why are Air Yeezys (Kanye West shoes) & Lebron 8 Pre Heat's so expensive?

Air Yeezys Go for between 800$  1050$

http://www.nicekicks.com/2009/03/nike-air-yeezy-release-date/

Lebron 8 Pre Heat's Go for between 700$  1050$

http://www.nicekicks.com/2010/10/nike-lebron-8-pre-heat-detailed-photos/