If statement to check for page template not working

I’m having trouble with adding some default text to my the_content field. I’m trying to set it up so I can have unique default text for each of my page templates.

When I place the following code in my functions.php file, and then add a new page, no matter which of my page templates I choose, the page editor field for the_content displays “this must be page.php”

Any ideas? (Thanks!)

<?php
add_filter( 'default_content', 'boilerplate' );

function boilerplate ( $content ) {
if ( is_page_template( 'front-page.php' )): {
     $content = 'this  is front-page.php';
     }
elseif ( is_page_template( 'leftmenu-page.php' )): {
     $content = 'this  is leftmenu-page.php';
     }
elseif ( is_page_template( 'notice-page.php' )): {
     $content = 'this  is notice-page.php';
     }
else: {
     $content = 'this must be page.php';
}
endif;
    return $content;
}
?>