Actually many have.
Tim Sylvia has tested positive for Clen
Chris Leben is still on suspention for Winny
Shawn Sherk, Stephan Bonner, Hermes Franca
Josh Barnet has tested positve in the past as well
Bas Rutten has but you dont hear much about it
Keven 'The Moster' Randleman handed in dog urine for his sample
Antonio Silva has as well