Webpack 4普及了吗，为什么大家还是在用Webpack 3？

现在已经2019了，Webpack官网甚至找不到3.x的文档了。
为什么各大库（Vue、Bootstrap）的文档、开发模板都还是在用Webpack 3.x呢？

例如Bootstrap官网：

再比如Vue cli创建的这些项目模板也是用Webpack 3.x的：

$ vue list
 ★ browserify - A full-featured Browserify + vueify setup with hot-reload, linting & unit testing.
 ★ browserify-simple - A simple Browserify + vueify setup for quick prototyping.
 ★ pwa - PWA template for vue-cli based on the webpack template
 ★ simple - The simplest possible Vue setup in a single HTML file
 ★ webpack - A full-featured Webpack + vue-loader setup with hot reload, linting, testing & css extraction.
 ★ webpack-simple - A simple Webpack + vue-loader setup for quick prototyping.