JTextArea - setText () and append () do not work in Listener () method

As the title says, I have a JList on the left side and a JTextArea on the right.

I set my listener for JList in the makeTextPanel () method as follows:

listSelectionModel = list.getSelectionModel();
listSelectionModel.addListSelectionListener(this);

where is the method called in the action event:

//This method is required by ListSelectionListener.
public void valueChanged(ListSelectionEvent e) {
    System.out.println("HEY");
    textArea.setText(null);
    textArea.setText("1: \n");
    textArea.append("2: \n");
    textArea.append("3: \n");
    textArea.append("4: \n");
    }

The event occurs because in the terminal I see "HEY", but nothing is printed in the text box. If I try to print a text field in the makeTextPanel () method after creating the text field, it will be printed. What's wrong? Why not print valueChanged events in the method? I would really appreciate it if someone could take a look at what I don't see here.

Full code: