All phones have stopped nightlies. They usually stop them prior to a stable release, or at least slow them down. No new features to possibly introduce more bugs, that way they can focus on the current problems and attempt to fix them. That would be my guess as to why at least.
I don't think the OG Droid is going to stop getting development from CM until ICS source code is released. Other devs I have no clue. Perhaps they build from Cyanogen, and since CM isn't updating they aren't. Perhaps the devs have been busy. Perhaps the dev has got a new phone, like the Bionic and has been busy playing with it.