They've decided that, some portion of the time, the single best search result they can return is whatever Google is returning.
Sounds like a very rational position. Anything less could be termed 'delusion' on Microsoft's part. And for the longest time, they were delusion about the search market in general. No longer.
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.
Google being an additional source of data for them does not equal Bing "giving up on bettering Google".