Challenge platform are a superb way to learn security practices, there are many challenges and walkthrough of different levels and with each one you manage to pass you learn a new thing. But there are several ways to get rooting a machine, get a flag, etc. That's why I created this website, as a site to share different unofficial write-ups to see different techniques and acquire even more knowledge. That is our goal and our passion, to share to learn together.
Also on TryHackMe it's the room author that must validate the write-ups submissions and very often the rooms are not maintained very long so the write-up you submit will never get accepted and listed on the page. That's why having an unofficial repository to list them is really helpful.
On HackTheBox you won't be able to share write-ups for non-retired boxes even if you share it password-protected.