Hi there,
Right now, this is by design. bbPress uses different template actions and filters than traditional WordPress posts and pages, to reduce the number of conflicts for the larger audience.
For some back-story, originally in bbPress 2.0, it was putting out sharing buttons everywhere — for forums, topics, and replies — as Jetpack was originally only built with posts and pages in mind. This wasn’t the intended behavior in bbPress, as sharing a single reply is like sharing a single comment (lacks context, etc…) so we opted to use bbPress specific filters to reduce conflicts with plugins (like Jetpack) that hook into WordPress’s ‘the_content’ filter, and make assumptions from there.
Fast forward to today, where some people do want this on a case-by-case basis. To enable this, a tiny stub plugin would need to be written to hook Jetpack’s sharing buttons onto bbPress’s content filters.
I’ll see if I can get someone to whip up some pseudocode for you in the next few days, if someone hasn’t written a plugin for this already. This isn’t the first time this has come up, so you may also want to search bbpress.org for other approaches and solutions.
