I think that many families today don’t have such strong mesorahs to begin with. With the transition from Europe to America, I think a lot got lost. Many people stopped being Frum altogether and later their grandchildren were chozer b’teshuva, and many others became more “modern” and their grandchildren “frummed out” In both cases, there was a break in the mesorah.
Amongst those who immigrated to the US after the War and retained their Yiddishkeit, as holocaust survivors many of them also probably lost some of their mesorah. Many of them were young when they lost their parents, and spending all those years in concentration camps, they could easily have forgotten their parents’ minhagim.
Also, in the US today, many people become more “Yeshivish” than their families and when they go away to Yeshiva, they may take on the minhagim from their Yeshiva.
I don’t know if it’s right or wrong, but my impression is that this is common.