[@r-a-y Keymaster 13 years, 5 months ago]

If you disabled search engines from indexing your site (under “Settings > Reading” in the WP dashboard), then bbPress will not add any activity entries to the site.

Here’s a ticket I posted on the bbPress site about this:
https://bbpress.trac.wordpress.org/ticket/2151

To override this behavior, add the following snippet to your theme’s functions.php:
add_filter( 'bbp_is_site_public', '__return_true' );