An Operating System is an structurally complex and convoluted piece of software that primarily supports different basic functions, such as executing an application or a program, scheduling tasks that are essential for its usability and stability, manage devices such as keyboard, mice, monitors, speakers, among other utilities that are given to the end user.
Most people are not aware that operating systems are a colossal engineering product that they use on an everyday life. From servers, to computers, to cell phones, and far beyond. Operating systems are created from the efforts of countless individuals across its existence. From Microsoft's employees creating Windows, and the open source community providing support to the Linux Kernel. Therefore, it is not unreasonable to infer that writing an Operating System is not a small feat, let alone for one individual. However, it is not impossible, there have been a few that managed to get some reputation in the community, for instance Temple OS.
Writing an Operating System from scratch is a challenge that many consider to be a waste of time and something only an insane person would do. However, where there is pasion, there is a community, willing to put time and effort into a project that most likely only a handful of people would witness. And for many, part of the process is to provide the experiences and knowledge they have acquired throughout the development.
Usually, this creates a chain reaction, where one individual would publish a piece of information, usually on the internet, for anyone to see, and this would inspire someone else to try and replicate it, or even create something else entirely. And hopefully, this new individual would also want to share their knowledge, and this could attract the attention from other people, further spreading the community's reach. Moreover, many consider that sharing newly discovered or refined content that emerged thanks to the work of others to be a gesture of "giving back to the community."