I married a BT, and I can tell you from my own experience, that you should not judge those who are leery. I wouldn;tt rade my husband for ANYONE, but there ARE problems inherent in the family dynamic, and some people feel that marriage under the best of circumstances is a challenge, so why add tension to the mix? When one side of the family is not frum, it creates a lot of stress when simchas come up. In the non-religious family, we had a situation where a close family member married a goy, and we were not forgiven for not attending the wedding. It took the death of a family member to heal the breach. It is also stressful that you can only visit one side for Shabbos and Yom Tov. The non-frum fo not “get” you and think you are always being a fanatic for simply keeping kosher. “Why CAN’T you eat with us at the diner? We’ll just have DAIRY!”
You would think that a generation away from that, people would not be so worried, when both baalei teshuvah’s kids are frum from birth. But even that is not “good enough” for some, because they have it drummed into them to marry the daughter of a talmid chochom, and the father of the boy does not want an am haaretz for a mechutan (not my words, and an unfair assumption for the boy’s father to make about the potential mechutan, though at times it is 100% true).