Microsoft has decided to keep the Cortana search function limited to using Bing and the Edge browser only for web results. This is in effect since the latest Windows 10 updates.
"Some software programs circumvent the design of Windows 10 and redirect you to search providers that were not designed to work with Cortana," Ryan Gavin, general manager of Microsoft Search and Cortana, said in a statement. In particular, they can interrupt some of Cortana's task completion and personalized search capabilities, he said.In response, Microsoft is locking down the Cortana search experience.
Remember, it's Microsoft's OS, they are just letting you use it. And yes, I realize that it really legally IS Microsoft's OS, it's just that they are making it a little more obvious since Windows 10 reached us.