This slump was to be expected when you think about it if not for the plane crash in 1961 the US women would have medaled at every Olympics for an unprecedented 52 years which not even the Russians have done in Pairs or Ice Dance ...
Possibly, as the loss of Laurence Owen, and so many other skaters and coaches in that tragic 1961 plane crash changed the course of figure skating history. Taking the baton from Carol Heiss, Laurence had the potential to win Olympic gold in 1964.
I'm not certain that it's accurate to say 'this slump was to be expected.' The podium drought is due to a variety of factors that have already been mentioned. Looking at the historical stats is eye-opening: U.S. ladies statistically still hold records for the most number of medals won at Worlds and Olympics. Sonja Henie of Norway holds the record number of individual medals won at Worlds and Olympics among ladies, with 10 World gold medals, 1 World silver medal and 3 Olympic gold medals.
U.S. ladies collectively have accumulated 26 World gold medals, 22 World silver medals, and 24 World bronze medals; added to 7 Olympic gold medals, 8 Olympic silver medals, and 8 Olympic bronze medals.
Ladies from the Soviet Union first broke through to the World podium in 1983 and to the Olympic podium in 1984. They also began winning in juniors, but it took them time to make more inroads. Oksana Baiul of Ukraine heralded a new beginning in 1993 winning gold at Worlds and gold at the Olympics in 1994. Then Irina Sutskaya won her first World medal (bronze) in 1996. The Russian ladies tried to wrest dominance from Michelle Kwan and they battled mightily but Kwan prevailed overall. But the Russians had begun to make their mark. After the reign of Kwan and her battles with Slutskaya, Butryskaya and the rest of the ladies field, the rise of Japanese ladies returned with a vengeance. Let's call it Midori Ito's revenge.

Of course, there was also the rise of Kim Yu Na, and Carolina Kostner hung around a lot picking up medals even before she caught up with her talent.
Russia stats: 7 total World gold medals (including that of Ukraine's Oksana Baiul), 8 total World silver medals (combined Soviet Union and Russia), 7 total World bronze medals (combined Soviet Union and Russia); 2 total Olympic gold medals (including Ukraine), 1 Olympic silver medal, 2 total Olympic bronze medals (combined Soviet Union and Russia).
Japan stats: 8 World gold medals, 4 World silver medals, 5 World bronze medals; 1 Olympic gold medal, 2 Olympic silver medals, 0 bronze (although they have a chance to add a bronze from this Olympics -- we'll find out shortly).
Additional historical ladies record medal dominance from other countries (aside from the singlehanded feats by Norway's Henie) include: Austria (17 World silver medals and 12 World bronze medals, 2 OGM - 4 OSM - 1 OBM); Great Britain (9 World silver medals and 7 World bronze medals, 2 OGM - 1 OSM - 3 OBM); East Germany (9 World gold medals, 8 World silver medals, 2 World bronze medals, 3 OGM - 1 OSM - 1 OBM). West Germany also has a few Worlds and Olympic medals in ladies (variously from Gundi Busch, Claudia Leistner, Dagmar Lurz, & Tanja Szewczenko, which I haven't combined with East Germany's stats).