Take, for example, an Italian or a Chinese immigrant family. The parents hold on to the old ways quite a bit. Their children less so. And their grandchildren not at all. The grandchildren are fully assimilated.
This is simply not happening with many Muslim immigrant families. And the West refuses to admit it.
And there is a lot of pressure on them to not assimilate, Muslims consider it to be treason. They are not there to integrate, they are there to ultimately conquer.