Because to confide a part of your soul to something that can think and move for itself is obviously a very risky business.
J. K. RowlingFinally, the truth. Lying with his face pressed into the dusty carpet of the office where he had once thought he was learning the secrets of victory, Harry understood at last that he was not supposed to survive.
J. K. RowlingHarry, despite your privileged insight into Voldemortโs world (which, incidentally, is a gift any Death Eater would kill to have), you have never been seduced by the Dark Arts, never, even for a second, shown the slightest desire to become one of Voldemortโs followers!โ โOf course I havenโt!โ said Harry indignantly. โHe killed my mum and dad!โ โYou are protected, in short, by your ability to love!โ said Dumbledore loudly.
J. K. RowlingThe Death Eaters can't all be pure-blood, there aren't enough pure-blood wizards left," said Hermione stubbornly. "I expect most of them are half-bloods pretending to be pure. It's only Muggle-borns they hate, they'd be quite happy to let you and Ron join up" "There is no way they'd let me be a Death Eater!" said Ron indignantly...."My whole family are blood traitors! That's as bad as Muggle-borns to Death Eaters!" "And they'd love to have me," said Harry sarcastically. "We'd be best pals if they didn't keep trying to do me in.
J. K. Rowling