It sounds as though the intent of the "dummy hammers" was to act as cocking indicators, since they were linked to the tumblers. The text mentions these guns are lever cocked, but doesn't mention whether the locks can also be individually cocked by using the dummy hammers. Personally, I'm not surprised they fell out of favor, and that shooters would prefer something less obtrusive.
I recall reading that many shooters were reluctant to adopt hammerless guns simply because most provided no indication if they were cocked or not.
