It's that Microsoft has no confidence in Bing. They aren't willing to trust their algorithms to produce the best search results. They've decided that, some portion of the time, the single best search result they can return is whatever Google is returning.
They've given up on trying to be better than Google, and are settling for being a cheap, off-brand knockoff that rebrands stale Google search results.
That's rather shocking, and I frankly thought the Bing team were better than that.