I've tried to the net to understand why Express uses MVC to structure the code, but I haven't really got any explanation. Can anyone please describe how Express can be used to structure codes that follows the MVC design pattern?
It's actually pretty simple.
You just modularize your code in different modules and folders and import/export with commonJS (require as import/export isn't yet that popular in Node).
You can create a model folder where you can place all of your schema declarations, a controller folder where you'd place all of your logics to handle the routes, a route folder where you'd place all of your routes (thanks to express router) and a views folder where you'd place all of your pug, ejs etc. files (if you'd like to make a server-side rendered app).
All the client-side code and static files usually go into a public folder and voilà, here is your MVC structure with Express.