If you ask around, you'll find that most of the people running Google Groups either hate or dislike Google Groups, however when their groups were first started it had a low-entry cost: it was free of charge and Google handled most of the annoyances of running a mailing list. New groups get added because it is still simpler than running your own mailing list.

http://ejohn.org/blog/google-groups-is-dead/

One should never underestimate the power of inertia.