Most of the reasons are on the “back end”, that you aren’t aware of. For the last 4+ years ACBS has had management of the list, as the kind volunteers that started it off no longer were able to keep up with it. The RFT (& ACT for Professionals) listservs are restricted to ACBS members (for the past 3+ years), but we’ve never had a way to deal with it (both with people joining and retiring) without significant staff time involved (because we wanted to keep spammers off, and had to verify ACBS membership of all new applicants). This new listserv interface handles that without staff effort.
Also though, we have the potential for being able to eventually host ALL of our SIG listservs on our website (as requested), facilitating networking, training, and scientific progress.