The Title field is required. What is the function of hiding this field in the form for? You cannot disable mandatory filling, you cannot set the default value (via UI). … or can you?
The ability to hide the Title field from the entity edit form is a bug ( Hiding required fields that have no default values results in an EntityStorageException (column cannot be null) when trying to save ).
You can set the default value for entity labels through the UI, for example, using the Automatic Entity Label module.