Provisioning new blog using wpmu_create_blog does not activate plugins

Hello
When I’m creating new blog using wpmu_create_blog function the plugin tables ( for example yop-poll but also on others) in database are not created, but when I go to Network Admin > Sites > Add New and create new blog manually the tables are created.
Example Code:

<?php
# Load WordPress barebones
define( 'WP_USE_THEMES', false );
require( $_SERVER['DOCUMENT_ROOT'] . '/wp-load.php' );

# Multisite domain
$main_site = 'example.com';

# Type of Multisite
$subdomain_install = false;

# URL param activated
if( isset( $_GET['new-site'] ) )
{
    # Create a new user
    $rand_number = rand( 1, 2000 );
    $username = 'user-' . $rand_number;
    $password = 'fake-password';
    // $password = wp_generate_password( 12, false );
    $email = "[email protected]";
    $user_id = wpmu_create_user( $username, $password, $email );
    // wp_new_user_notification( $user_id, $password );

    # Create site
    if( $subdomain_install )
    {
        $newdomain = "{$_GET['new-site']}.$main_site";
        $path = '/';
    }
    else
    {
        $newdomain = $main_site;
        $path = "/{$_GET['new-site']}/";
    }
    $title = $_GET['new-site'];
    $blog_id = wpmu_create_blog( $newdomain, $path, $title, $user_id ,
array( 'public' => 1 ) );
    echo "New blog with ID = $blog_id";
}
else
    echo 'Add to the URL: <b><tt>?new-site=NAME_OF_THE_SITE</tt></b>';