Taking a complete example of something and changing it to fit your needs is far easier than making something to work from ground-up using underlying technologies.
This is because starting from the example limits the amount of things you need to learn at the same time. Both in the sense of
number of technologies
and in a sense of figuring out how they interact with each other.
You're able to focus on the small change that you care about instead of getting bogged down in the infrastructure setup.
discoverability is a very important part of how easy it is to adopt new technology. Examples serve as a kind of "discoverability aid" - they don't really improve the "natural discoverability" but they give you the rails to hold on to while you fumble in the dark for understanding.