|Quoting flyby519 (Reply 49):|
They could, but there would be difficulties finding good infrastructure like gates/terminal areas. Also every time DL tried to add MIA capacity AA moves onto the route with overcapacity and destroys the fares. DL buying the AA MIA hub would eliminate any real competition in the MIA airport, so that is were the value comes.
And it's probably cheaper in the long run to buy a ready made hub rather than trying to build it piecemeal.