Pretty simple I think - it just didn't sell. There really isn't any other reason to stop making them.

As to why they didn't sell, there are many opinions, including the ones you listed above. My personal opinion is that the typical J frame buyer wasn't interested in the 9MM revolver because it is more complicated to use then a 38 special, and potentially prone to more problems. A lot of these buyers only buy one gun, and rarely shoot them.

I think it is easy for those of us that shoot a lot and are into guns to forget that. This is something I am reminded of every time I teach an NRA class and deal with a new shooter. A revolver can be complicated enough without introducing moon clips.

My personal experience with the 940 has been good and bad. I have two; one has always shot very well and extracted properly. The other one jammed the cylinder and had rough extraction. I sent it back to Smith & Wesson, they fixed it for free, and I have never had a problem with it since.