Dream teams aren't always a good idea. If you could magic together Rowling, Tolkien, and Lovecraft, could they produce a work that bettered their individual efforts? If Wozniak, Bushnell, and Sinclair had grouped together in the early 80s to build a computer, would it have been better than their individual efforts?
I don't know the answer but my personal hunch in both cases is "no" because the potential for personal glory and realizing an individual vision is diminished significantly. That doesn't drive everyone, but it drives enough of the greats to be relevant.