I assure you that every scientist wants to clone the mammoth. Cloning is beastly hard. Once the cloned cell is achieved, it then must be implanted in the womb of an elephant to grow and finally be born two years later. The female elephant must be willing and fertile. Animals are not like young human females that can get pregnant every month. Animals must be "in heat" to become pregnant. Overseeing the impregnation and the gestation process is about as challenging as the cloning. That is why it may be a long time before we achieve Jurasic Park.