Because it's very dangerous. Simply having a compiler which puts structures in another layout or adding a field to the object is enough to render all your previously generated files useless.
If you just want to save and load data, I would rather serialise it([https://nim-lang.org/docs/marshal.html](https://nim-lang.org/docs/marshal.html) ). If you want something more compact then e.g. JSON or YAML take a look at msgpack: [https://nimble.directory/pkg/msgpack4nim](https://nimble.directory/pkg/msgpack4nim) (note: I haven't used msgpack with Nim, but I had good experiences with it with other programming languages)
