The good components, and the docs are the biggest reasons. But also it's a very well thought through thing based on web specs, using html technology. People can get useful work done almost right away, and what they made is self contained by default, limiting their damage. It also works for the document case, AND the single page app case. Want to make a landing page that converts well? Vue has your back. Want to use that one jQuery plugin, because it's awesome... Vue can do that easily - it plays nice with others.

React should copy it more, and copy web standards more.