Drag & Drop feature for customizing UI on modern web applications

Many web applications that allow you to design website have drag & drop features that allow you to rearrange the layout as most of the components are modular. There are also many web applications that allow you to change labels in an 'edit-mode' on the fly.

So I am curious why most modern web applications don't support features where the users can change the layout for web applications (unless they resize the browser window) or allow users to rename labels to something that they are more familiar with. It would probably be a good alternate strategy to trying figuring out what the best layout and labels are for users, especially if you have a very diverse group of users with many different preferences.

Question: are there examples of web applications with drag & drop features for customizing layout?