First, you are welcome to challenge the premise that there is in fact less respect for parents in the United States. But if it were true, what might be the possible mechanisms?
1. American parents have less time to discipline their kids, in part because women are more likely to work, wages are higher, and there is a general rush and hurry.
2. American culture is less closely tied to the entire notion of hierarchy and respect, whether or not kids are in the picture.
3. The American divorce rate is relatively high.
4. Balance is difficult, and a tipping point requires that someone be in charge. In America that is the kids, although the underlying reasons for this difference may be quite small.
5. America is saturated in mass media, and that culture encourages the independence of the child, most of all because children are prime viewers of TV and drivers of Nielsen ratings.
6. Americans are more mobile, and thus less likely to live near grandparents, support structures, and other mechanisms of norm enforcement.
7. It is simply a time trend. Americans are ahead of the rest of the world but everyone else is catching up. Give them time, it’s just like how we will all come to resemble California someday.
8. "In America it depends on how parents behave and whether particular parents deserve to be treated with respect. Parents don’t get respect automatically just because they are parents." I’m not going to tell you who said that one.
9. Some other notion of American exceptionalism.
Your views? Google appears to yield few answers to this question or even attempts at an answer…