Planet Earth: Temperate Forests had a segment on pandas. Apparently, they can only nurse one baby every several years, and even devoting all of their time to nursing a baby may not be sufficient to sustain it, as bamboo apparently makes really thin milk.

Also, if a panda has twins, she has to abandon one outside her den. I cried during that episode. It shows a panda in a den holding the little baby and nursing it. The mother looked really frightened and sad. It was really distressing to watch.

So, a combination between a very slow, unreliable mating cycle, and destruction of habitat by the massive demands of the Chinese economy have created a situation entirely unsuitable for pandas.

because people put them in zoos,kill them for the fur,destroy their habitats,and just plain hunt them