Why does the process remain in the manager after closing the program?

Question

C++ / C#

Main form code:

public partial class Main : Form
    {
        public Main()
        {
            InitializeComponent();
        }

        private void panel1_Click(object sender, EventArgs e)
        {
            Employees_Table employees_Table = new Employees_Table();
            employees_Table.StartPosition = FormStartPosition.Manual;
            employees_Table.Location = Location;
            employees_Table.Show();
            this.Hide();
        }

        private void panel2_Click(object sender, EventArgs e)
        {
            Halls_Table halls_Table = new Halls_Table();
            halls_Table.StartPosition = FormStartPosition.Manual;
            halls_Table.Location = Location;
            halls_Table.Show();
            this.Hide();
        }

        private void panel3_Click(object sender, EventArgs e)
        {
            Films_Table films_Table = new Films_Table();
            films_Table.StartPosition = FormStartPosition.Manual;
            films_Table.Location = Location;
            films_Table.Show();
            this.Hide();
        }

        private void panel4_Click(object sender, EventArgs e)
        {
            Tickets_Table tickets_Table = new Tickets_Table();
            tickets_Table.StartPosition = FormStartPosition.Manual;
            tickets_Table.Location = Location;
            tickets_Table.Show();
            this.Hide();
        }

        private void panel5_Click(object sender, EventArgs e)
        {
            Sessions_Table sessions_Table = new Sessions_Table();
            sessions_Table.StartPosition = FormStartPosition.Manual;
            sessions_Table.Location = Location;
            sessions_Table.Show();
            this.Hide();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }

When opening a new form, the main one is hidden, and when closing a new form, the main one is opened:

private void Employees_Table_FormClosed(object sender, FormClosedEventArgs e)
        {
            Main main = new Main();
            main.StartPosition = FormStartPosition.Manual;
            main.Location = Location;
            main.Show();      
        }

And after I close the main form, the process remains hanging