Because it is a hand most people have a hard time walking away from. It should not be too hard to fold if you see you are beat, but people would rather lose their whole stack and sink with JJ than believe another person paired the A, K, or Q. In their hand. Even more embarassing, you guess correctly, villain has no A, K, or Q. They flop a set with low cards, complete a straight, or hold the flush. And you rebuy, because you believe JJ is the nuts with no face cards on the table. And villain shows, um, that you do not have the nuts.
__________________
|