It's better to fork an existing coin rather than staring your brand new blockchain. I advise you to choose a PoS coin as it's way easier to manage, run nodes etc. Otherwise you will need to have miners to verify transactions, sync blockchain etc.
The point of coding your own blockchain is not to lunch your next altcoin and try to get rich of it. As blockchains can be used for all different sorts of things you can play by building one. By following such tutorials it can help you develop the coding skills or even sharpen the existing ones. It is not all about creating the next altcoin, but for educating purposes to see how this structure work. It can be complex task, but while learning you want something simple to see how it works and ways how it is implemented and understand the core principles behind it.
You could also want to build some small centralized blockchain for your small project or even of some company, limitations are endless. Building blockchain is not strictly tied to building next altcoin as money is just one application that can be built on top of it.
This is my exact intention of this tutorial.
Spot on.
There is far more to the Blockchain than $$$ the immutability in itself is the key to innovation and further development of it.
The more we can get at this grass roots level the better the next and current generation can understand it.