They plan to rewild the mammoths to slow the melting of the permafrost in the Arctic tundra.
Just a convenient excuse for their "Pleistocene Park" fantasy. The idea is that herd animals can help slow the melting of permafrost.
But there already are plenty of Arctic herd animals. It's just that their numbers have been depleted. If they really cared about the Arctic tundra they would concentrate on what can be saved now.