The function is disabled, since it uses additional resources.

On a related note, that function might actually discourage some folks from participating, since they may be fearful of being seen reading a particular thread and/or not responding right away; yes, I realize one can track what one is doing by viewing one's user profile, but that takes effort and is somewhat inaccurate.

In a nutshell, that function is disabled primarily to conserve server resources and to a lesser extent for visitor privacy.

With all that said, it may enabled sometime in the future if enough folks truly desire that feature.

Thank you for the suggestion.

Ron