In a typical open source project only one person has had a look at a particular piece of code. Only in the larger and more mature projects do people actually spend time reviewing code. Also, if you don't pay for the free code, there is often no serious recourse to recover your data either.

As stated in my first comment, Obsidian does not support Emacs keybindings properly, nor is it open source. Writing an extension to add Emacs keybindings is not at all trivial, because you have to work around a lot of existing and undocumented functionality.

There are other reasons for not vibe coding your own alternative, but as LLMs keep progressing, these reasons may become less relevant.