Losing touch with family

As my Dad comes up to the "Big 100" at the end of the month, I have been researching his mother’s family for a possible book and I have just made contact with another family that has been lost to us for a couple of generations.
Andrew Stewart came to NZ and stayed briefly with Dad’s family in Lower Hutt in 1931. After that we know next to nothing of them except that he was supposed to have married Alice, a part-Indian woman. Although we kept in touch with Andrew's sister’s family for two more generations, Andrew and his family dropped beneath our radar. Until I called last Saturday there had been no contact for all that time.
That’s a pity because Andrew went into exactly the same trade as my Dad: they both made upholstery for the vehicle assembly business , Dad in Lower Hutt and Andrew in Auckland. I think they would have enjoyed each other’s company.
Why did we lose touch, I wonder? I suspect it may have been to do with Dad's parents' deep, if conservative commitment to the church, and I am saddened about the fact that they might have let the church come between them and their distant relatives.