In an ideal world, this would be pointless because if the code requires "annotations", it should be rewritten, or annotations may be just a specific kind of com

In an ideal world, this would be pointless because if the code requires "annotations", it should be rewritten, or annotations may be just a specific kind of comments in the code itself rendered in a specific way. But in the real world, I think, the use case for annotations is when one group of people writes code, and another group of people annotates it because authors and collaborators can be opinionated, stubborn, lazy, or too busy, or there may be too much bureaucracy on the project, so it is much more realistic to just put annotations on some third-party website than to try to collaborate with the authors to add comments in the code or refactor it.