I think after Bill Ruger passed away, the company lawyers wanted nothing more to do with a revolver that couldn't be adapted to Ruger's transfer bar ignition.
It only was in production so long because Bill Ruger liked it so much.
The Number 1 single shot rifles were another one of Bill's pets.
It's sort of like Ford Motor Company having to wait until Henry I died before they could finally drop their old flathead V-8 engine.