How'd everyone forget this? He didn't want Obito to go to the dimension because Obito had that rinnegan eye which Madara was trying to get. Now Obito can just take and crush the eye now that he is in the dimension.
Madara found Naruto impressive and has a respect for him, but he did not find him frightening by any means. As people have said, he wants Kurama and his eye back.