I shudder to write those words, but the facts speak for themselves. Take a look at the raw numbers:
Using data from Wikipedia, I plotted the Nielsen shares of all daytime dramas airing at least one season on a major broadcast network (CBS, NBC, ABC) from 1952 to the present. Each line represents a single program. The side axis represents the share of all daytime viewers as measured by Nielsen.
As you can see, recent years have witnessed an almost linear downward slide in the ratings of all soap operas, not to mention the absence of the lively competition for daytime viewers that peaked around 1970. It is interesting to see how nearly all the soaps (except for Y&R, which has double the viewers of its closest competitor) closely track each other on this downward slide. Even Y&R has seen a similar rate of reduction in its viewing audience, but from a higher baseline.
Though it appears that most successful soaps over time experience a large gain in viewers at the get-go, with a long and gradual tapering off at the end of the tail, it is apparent that macro-trends of decline begin to affect all programs within the 1988-94 period. From 1994 onward, declines commenced in earnest.
The instigators were likely thus:
1988 - writer's strike
1994 - OJ Simpson trial
Also, the increasing availability of alternative programming streams (cable, internet) and TiVo use have played a background role in all this.
Here are breakdowns by network:
CBS soaps got a head start and dominated the ratings charts for years. Virtually all of them performed well, and many all were P&G productions in the classic era. As the World Turns was America's top rated soap for two decades. Gradual erosion of P&G market share due to the birth of newer, more daring soaps, plus the advanced age of its serials doomed most of the longtime veterans on the CBS schedule to extinction by the 1980s. The Young and the Restless, premiering in 1973, remains a strong performer however.
Of the big three networks, NBC has had a relatively weak daytime drama lineup over time, relying more heavily on game shows in the past to fill the daypart's airtime. The NBC Daytime glory age was roughly from 1967-75, when its top rated soaps Another World, The Doctors, and Days of our Lives comprised the core of its lineup. All three soaps suffered greatly from NBC's late 70s-early 80s collapse, and NBC Daytime has never truly recovered. Only one traditional program (Days) remains in the daytime hours currently.
From being a non-participant in the daytime race, ABC came to dominate daytime in the late 70s through the late 80s, due to the stratospheric success of its core soaps (and overall lineup) during that time, especially General Hospital. However, it has been all downhill from there since that brief early 80s peak. Note the mid 70s trough for GH (which took it to last place on the ABC schedule!) that led to the reign of Monty and the subsequent dramatic changes that changed the face of daytime, for good or ill.