The hook declaration takes 6 parameters, yet none is in your function’s definition. Also, before calling the hook wpmu_new_blog, WP does a restore_current_blog(), so it’s safe to assume that we have to switch to the destination blog before inserting content.
add_action( 'wpmu_new_blog', 'new_blog_wpse_115724', 10, 6 );
function new_blog_wpse_115724( $blog_id, $user_id, $domain, $path, $site_id, $meta )
{
$current_blog_id = get_current_blog_id();
switch_to_blog( $blog_id );
$samplepage = array(
'ID' => '2',
'post_name' => 'about',
'post_title' => 'About',
'post_type' => 'page',
'post_author' => $user_id,
'post_content' => '<p>Write something about your business. This may include but not limited to what you sell, what are your target audience or market, who you are, your objectives, background history and your location.</p>',
'menu_order' => '1',
'post_status' => 'publish',
'comment_status' => 'closed'
);
wp_insert_post( $samplepage );
switch_to_blog( $current_blog_id );
}