I fully understand those who are wary of marrying/marrying their kids off to children of BT. Parenting is taught by example, and BTs (due to no fault of their own) have little to no knowledge of how to run a frum home. They can be and often are wonderful parents, but they’re starting from scratch when it comes to frum parenting. This is probably the reason why it is more common for children of BTs to go off the derech: the parenting in a BT home is a first attempt, with no previous training.
Caveat: I said I understand those who are wary of marrying/marrying their kids off to children of BT; not that I feel this is the correct way of doing things. I do not.