Why are cats blessed with the superior intelligence to know everything but do not have opposable thumbs and we have to be served by those with opposable thumbs who have no brains?

Because it gives those who serve us a purpose, and without purpose, they're just that much more useless. They got the thumbs and we got the brains; if we'd gotten thumbs and brains, then people never would have figured out why they're here. Because, you know, we got the brains...