of trying to find out what is wrong with you, rather than what is right about you. They want to answer the question "why should I NOT hire you?", rather than "why should I hire you?".
Most of us are uncomfortable with that approach.
Edited:
I'm in the tech industry, and the trend has moved to testing candidates, rather than having conversations. Online tests, whiteboard coding exercises, solving puzzles in an interview, questions that attempt to "stump" the guy being interviewed, etc.
It's all ridiculously flawed.