There is another reason it is not done. Cost. A solar ammonia system big enough to cool a typical house would be so expensive that if you put the 5-7% interest it would cost to finance it against the utility bill from a standard DX package you would be losing money. Ditto if you paid cash. You could make enough in interest by investing the money to more than pay your electric bill. Your investment would never pay for itself. Plus how many people like looking at a big industrial scale mess of mirrors and pipes in there backyard. OR in their neighbors back yard. Add in the possibility of having to evacuate the neighborhood if there is a leak and your insurance company would have kittens.
You are correct. Though quite safe, it's still possibility of leaking. Safety, i think, is the most common factor when someone thinks about ammonia system.
Here is article in Ashrae Journal - "Ammonia Future", it talks a lot about Ammonia as a trend in using refrigerant.