Why specify the full path to the js file if there is tree shaking?

Question

webpack

Good afternoon, I look at the manuals and a lot where this design is used:

import AppBar from '@material-ui/core/AppBar';
import ToolBar from '@material-ui/core/ToolBar';
// тут еще 20 импортов таких же

Why not use instead:

import {
  AppBar, 
  ToolBar,
  // other
} from '@material-ui/core';

If there is tree shaking, why specify such paths?
Lessons and manuals are not so old, then there was already webpack tree skaking

Answer 1

Export through brackets - named:

//module.js
function myModule() {...}
export { myModule }

//other.js
import { myModule } from 'module.js'

Export via name - default:

//module.js
function myModule() {...}
export default myModule();

//other.js
import myModuleOtherName from 'module.js' //  для default можно использовать любое имя

Here's the full description: https://learn.javascript.ru/import-export
This has absolutely nothing to do with tree-shaking. If it does not work, the cause must be sought elsewhere.