All I can say is birds are weird. As the above response stated its a possibility that your macaw simply doesn't like the flooring at your house. Maybe there's something like a plant that your macaw is afraid of. It really could be anything. I've stopped trying to understand bird logic as they tend to dislike things so randomly.
I would still do your best to put your macaw on the floor, and give lots of treats and praise for being there. Helping your macaw overcome fears, and learning to adapt to a new things can be so beneficial. For an example my Ekkie will not take treats, or food from anyone else but me. He has bonded to me, and refuses to eat for someone else for some odd reason. I felt flattered at first, and then I realized that if something ever happens to me no one will be able to babysit Nico.
