Yes, this indeed looks like laziness of the developers to me. When the app was developed, JavaFX came pre-packaged with the JDK/JRE, so they still rely on it. Today, it should perhaps just be a regular dependency of your app and be part of your app.

If I were to build a Java desktop application today, I would even bundle the entire JRE, since you cannot assume that it is installed on most desktops anymore.