Configurable fields are always added to the root structure of entity forms and their form element names equal the name of the field itself. The same was not true for node base fields on the node form. The element corresponding to the author user (named 'uid' among the base fields) was located at $form['author']['name'], the revision log message (named 'log' among the base fields) was located at $form['revision_information']['revision']['log']. This made it impossible to handle base fields and configurable field widgets in similar ways. Therefore all base field form elements have been moved to the root of the form and renamed to use the base field name for the element, ie. $form['uid'] and $form['log'] respectively for the above examples.
The list of base fields can be found in the baseFieldDefinitions() implementation of the Node entity class.
The respective changes in core/modules/node/src/NodeForm.php's form() method are
| change | was | is | new group |
|---|---|---|---|
| moved | $form['revision_information']['revision']['revision'] | $form['revision'] | revision_information |
| moved | $form['revision_information']['revision']['log'] | $form['log'] | revision_information |
| renamed and moved | $form['author']['name'] | $form['uid'] | author |
| renamed and moved | $form['author']['date'] | $form['created'] | author |
| moved | $form['options']['promote'] | $form['promote'] | options |
| moved | $form['options']['sticky'] | $form['sticky'] | options |
