Use page title as set in admin area on BP directory pages.

bp-page-title.php

/**
 * Use page title for BP directory pages.
 */
function my_set_bp_page_title() {
	// Check to see if current reset post is a BP directory; if not, bail.
	if ( false == in_array( $GLOBALS['post']->ID, bp_core_get_directory_page_ids() ) ) {
		return;
	}

	// Use WP page title for the_title().
	$GLOBALS['post']->post_title = get_post_field( 'post_title', $GLOBALS['post']->ID );
}
add_action( 'bp_template_include_reset_dummy_post_data', 'my_set_bp_page_title', 50 );

/**
 * Use page title for <title> tag on BP directory pages.
 */
function my_set_document_title( $title ) {
	// Not a BP directory page? Bail.
	if ( false === bp_is_directory() ) {
		return $title;
	}

	// Set page title to use post title.
	return $GLOBALS['post']->post_title;
}
add_filter( 'bp_get_directory_title', 'my_set_document_title' );