Why my button element don't trigger the submitForm method?
Your first "submit" button doesn't get recognized by Drupal as a button because you use an inline template.

If you want to add a class on your button use:

$form['submit'] = [
  '#type' =&gt; 'submit',
  '#value' =&gt; $this-&gt;t('Submit'),
  '#attributes'=&gt; ['class'=&gt;['glyphicon', 'glyphicon-search']],
];