They don't know if it was climate change, inbreeding, but they assume the ice age played a part in it, and they were hunted by homosapians, but not to extinction.
The scientist that cloned dolly says they could use two ways to clone a mammoth, one they could take an elephant egg to grow an embryo(similar to how dolly was cloned) , and create embryonic mammoth stem cells. They say that they want to consider doing this, but what if they have tried and haven't said anything?
If the mammoths really died off, then how do we have elephants since they are descendants of mammoths, so therefore to have descendants like we are to apes, then they evolved not went extinct, elephants are just a more evolved mammoth.
Mammoths remains haven't been found in Austrailia, or South America, could they still roam there, just not have been found? We never know. Nothing ever really dies out, cause in a way technology has progressed so much they could have cloned one and just haven't said anything. Or they have found one and won't say anything. They kept finding Amelia Earhart's plane so they could get keep getting funding, whose to say that they don't want to quit getting funding for research?