I have a different theory regarding US ladies: The US hasn’t gotten noticeably worse. Rather the rest of the World has caught up and in several cases, has passed by the US.
Going way back, we have had stars like Hamill, Yamaguchi and Kwan, but if you look at US ladies who were
not huge stars but were the US no. 1 in their respective olympic cycles, they were just as wobbly as the current batch - Rosalynn Summers, Elaine Zayak, Tiffany Chin, Debi Thomas, Jill Trenary, Tonya Harding, Nancy Kerrigan, Nicole Bobek, Sasha Cohen, and then everyone after 2008. They were skittish competitors, but the competition was a lot less fierce. Then Mao and Yu Na arrived on the Senior scene (two big stars), so it's revealing how US ladies still achieved podium finishes until 2007 despite a shaky performance here and there, because they only had to contend with only one foreign star who was more talented than they (only very occasionally two) at any given time before Mao and Yu Na (Ex - Witt, Ito, Baiul - that last one is questionable

)
I also don’t think the USFSA ever fully and completely recovered from the elimination of 6.0 and emphasizes safe programs to an extent. It can work rarely (Lysacek - 2010) but that doesn’t really win under IJS anymore. Our most high profile coach Frank Carroll was big on not allowing his students to place a jump in a program unless it had a 90 percent success rate. Trapped in 6.0 mentality
Parental interference is discussed. That could be a factor too: They pay big money and want a say even if their opinion is not grounded in reality. *Cough* Nathan Chen *Cough*