Why not include a basic html ? (Git general usage)

[GitDoggo]

I'm new to git, and I really don't understand the concept of the "here's an example you can run ! except you have to do 34886 unnecessary manipulations, and add things to your own files ! enjoy !"

I understand I have to npm install, get grunt etc., but why can't you put functioning files ? like a basic html to have a base to work on, and the main.js even if it's very basic ? I managed to make a basic file by using your demo html source code but when you say "Then call the html5_qrcode function on thediv" and throw some code without saying where it should be I don't know what to do and I feel like you could have put it in the file in the first place.

A lot of git repos are like this one, incomplete, necessitating hundreds of manipulation that could have been included, and more than vague instruction. Is it a common habit ? Is it a thing so that people that don't really know what you're doing can't reproduce your "example" at home ?
I could really use some explanation (on the git usage as well as on how to make the example run), because maybe you think it's clear but for a newbie it really isn't