Why are custom widgets not previewed in the Flutterflow editor before app build or at design time?

I have some custom widgets that work.

One is an image and video viewer.

Another is a widget that allows you to create texts that when clicked on in a sentence show a popup.

Both widgets work when I compile my app or run the test mode. But in my Flutterflow editor I can't see them. Instead, they only appear white or grey. Is there a way to be able to see the custom widgets in the Flutterflow editor or is it impossible? Why is it not possible to see the custom widgets in Flutterflow?