Earlier quoted context omitted.
Microsoft is trying to drive traffic to Bing (and their other services). The rendering engine doesn't actually matter. Microsoft could just bundle Chrome with Windows but instead they are specifically taking the Chromium engine and putting it in an Edge shell. The only reason for that is to maintain control over the user to drive them to Microsoft properties.
> The rendering engine doesn't actually matter. It does matter. From the comment above "browser vendors taking the lead over standards committees" means influence on where the technology is heading, specially for rendering engines. Remember how long it took IE to implement canvas? This was a way to avoid a new "OS" over a OS (Windows)
Also I suspect Microsoft will have far more actual influence by driving development of Chromium than with their own rendering engine. It's pretty hard to drive new standards when you are barely achieving the current ones. Microsoft's focus on Electron for cross-platform development kind of informs this move as well.