Laravel does routing for you. Do you know how to make that from scratch?
Wordpress have plugins for galleries and blogs. Could you implement one?
Blaze, angular and many others allow you to include blocks of HTML and parse them based on server-side information. What about doing it yourself?
Meteor has an amazing form-builder based on schemas (autoform). Do you think of a way of doing something like that?
This website itself is a proof of concept around IDEAS, not technologies.
I'm not 'reinventing the wheel'. The goal is not to imitate what those amazing frameworks/libs are. It's just to see if I'm capable of creating something like it.