Bing powers a host of other engines. Yahoo, DuckDuckGo, most of Qwant, AOL, the web results from Windows Search, Ecosia, and others are all dependent on Bing's search APIs.
If you use a Google alternative, there's a good chance it's just Bing under the hood. So this leak could be a pretty big deal.
There is a reason why they hide that code ^^
My guess is that they did not leak Windows and Office source code because they want to mine it for 0days themselves.
Time to really lock things down folks.
Or simply because (as the screenshot show) they got only access to Azure for an account that doesn't have access to the OS department of Microsoft