I think there is a special value in open source when it comes to a personal knowlege base. We invest so much time in it, and we need to know that it's not going to be taken away from us, or made unaffordable. I made https://www.asnotes.io (basically obsidian with markdown and nested wikilinking in a VS Code extension), because I wanted and thought others would want something that is a) open source and b) version control friendly so we don't even have to rely on a sync server being there in the future.