Maybe because Angular material components are much better than material-ui?
material-ui's tutorials are really bad examples on this. They teach you to import from specific dir path inside material-ui. (e.g. import Pen from 'material-ui/lib/pen' or whatever)
Instead, they should recommend: import { Pen } from 'material-ui' since most of their exports are already in material-ui/src/index.js file (or some index.js file from package.json's main part)