Firstly Joplin is great note taking app and if that is all you want you really should go for it. I used it for years and was really happy.

But Obsidian is far more than just a note app. It like a Wikipedia page, you can add links within the text of your notes to another note. But they are also bi-directional, meaning you can see the incoming and outgoing links.

Making easy to use the related notes instead of just link to it. Sometimes you did not even think this note could use that note information and it shows you can connect them.

Not only that Dataview lets you live index and query your data. Letting me build a template and query that data dynamics.