Access meta box checked value in another file

You haven’t quite got a grip on the switch statement, read up here.

$template = get_post_meta( get_the_ID(), '_my_theme_post_template', true );

switch ( $template ) {
    case 'template-2':
        get_template_part( 'inc/post-loops/template-1' );
        break;

    case 'template-1':
        get_template_part( 'inc/post-loops/template-2' );
        break;

    default:
        // Neither values matched, do something else?
        break;
}