I heard a radio interview a few months back with these guys. The question was, as pointed out above, why? Just because we can doesn't mean we should. Yes there were commercial reasons, but 90% of their answer came back to restoring the environment, undoing the damage mankind has done over the eons. I'm not going to judge their motivations, and I have near zero doubt of their ability to follow thru. My focus is on what the impact may be - good (as they intend) and bad (as they may not aniticipate).
FYI, it's not just the Woolly Mammoth they are targetting right now. Their current species list targets 3 animals (
more explanation on each here) - Woolly Mammoth (as elephants are still close enough to be used for insemination), Tasmanian Tiger, and the Dodo bird. There are others further out on the plan, and they point to other species being brought back prior to this effort (Florida Panther, Black Footed Ferret, American Bison).