Cause fudge didnt want to believe voldy moldy might be back so he didnt give him anything that could have proved he´s right

Plus he's a minor, and i'm pretty sure snape mentioned it was illegal

@Springle04 I'm talking about Harry putting his name in the Goblet of Fire

Well, as his name have been chosen for the tournament and thus cannot escape, there isn’t really any point to use a expensive arguably inhumane potion.