1. With WebGL support and the other new features in IE11, they are close to finally being comparable to Chrome and Firefox in terms of being a modern browser. Yes, bridges were burnt, but IE11 and things like TypeScript are making Microsoft cool in the web space again.
2. Previews appear to show IE11 is also competitive in terms of speed with other modern browsers. (IE was already fast at 2D canvas, but not much else.)
3. The tech community was disturbed by the NSA spying scandals (that involve most major browser vendors), which led to some movement to switch to alternative browsers and search engines. Even if people don't switch entirely away, they might choose to put less eggs in one basket, so prefer to not do Chrome+google.com or IE+bing. Of the other combinations of those options (there are others of course, but just considering those), IE+google.com seems more likely than Chrome+bing, so IE might gain a little there.