And obsidian is not open source either. If you rely on any of the functionality besides just raw text editing, you may lose it one day.
I don't understand how the benefits of open source are so easily downplayed.
also, it's not unreasonable to think that a compatible alternative would be easier to build compared to a less standard format
What do they do besides the frontmatter (which is fairly trivial to process or ignore in a hypothetical future where one wants to stop using obsidian)?
My notes, which can include things like my location, appointments, plans, things I don't want a random company viewing never leave my device, which is the only way you can be sure they are not being viewed without an oss app.