Why some fields show up in the class inspector in the project folder and some don't?

I noticed that if I create a Sprite field, it will appear in the inspector when I click on the object class in the project folder, but the other fields like float are not. Why so?
It would be very convenient for me if I could set some values directly in the class in assets, but I guess the only way to do this is to use SO.

There are rules to whether things can be serialized, I have a resource that should cover all of them. Serializing a field, I’ve not updated it in a bit so it could be a little scrappy.

If you’re referring to the fields that you see when selecting a script asset, those are default reference fields that get set when making an instance of said object in the editor only. It’s only available for Unity object references.

Script assets aren’t an actual instance of an object. They’re just text files.