Why does the JScrollPane show up but not its scroll bar?

Here is my code. The JScrollpanel shows up but now the scrollbar. I also can't use the scroll wheel if the text goes below the area.

JTextArea textArea = new JTextArea("Enter text here");
textArea.setPreferredSize(new Dimension(100,100));
textArea.setLineWrap(true);
textArea.setEditable(true);
textArea.setVisible(true);
JScrollPane scroll = new JScrollPane(textArea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

//frame
this.setTitle("GUI Practice");
this.setLayout(new BorderLayout());
this.setResizable(true);
this.setSize(720,480);
this.setLocationRelativeTo ( null );
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

this.add(scroll, BorderLayout.SOUTH);
this.setVisible(true);

Never, never, NEVER do this:

textArea.setPreferredSize(new Dimension(100,100));

You are artificially constraining the size of the JTextArea, and you yourself are causing the JScrollPane to fail. Instead, set the JTextArea's column and row properties.

e.g.,

import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.*;

@SuppressWarnings("serial")
public class GuiPracticePanel extends JPanel {
    private static final int ROWS = 10;
    private static final int COLS = 80;
    private static final String INIT_TEXT = "Enter text here";
    
    private JTextArea textArea = new JTextArea(INIT_TEXT, ROWS, COLS);
    
    public GuiPracticePanel() {
        JScrollPane scrollPane = new JScrollPane(textArea);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        
        setLayout(new BorderLayout());
        add(Box.createRigidArea(new Dimension(400, 300)));
        add(scrollPane, BorderLayout.PAGE_END);
        
        textArea.selectAll();
    }
    
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            GuiPracticePanel mainPanel = new GuiPracticePanel();

            JFrame frame = new JFrame("GUI");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(mainPanel);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }
}