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Linux also always allowed you to install applications directly. Everyone just uses package management software at this point because it’s all well managed and easier to keep things updated, but you can still install things manually with make.
You only need make if you’re compiling. Installating precompiled software is somewhat easier, since it’s basically just copying to /bin. If you know where that is, then it’s simple.
Markdown is also an open format. You aren’t forced to use Obsidian for everything, and there are already numerous programs that are capable of displaying the formatted end-file, because it’s standard markdown.
It’s not some proprietary thing that only Obsidian uses.