It's not based on much more than stereotypes and ignorance that reminds one of Medieval peasants and their feelings about black cats or walking under ladders. Or, Texans thinking Jews have horns. There is a lot of blind following in the frum world and silly ideas about BTs and bad family backgrounds are one of them.
I won't even bother picking it all apart except to say I know many FFBs with family problems and many BTs from sound families. I also think we talk about family background too much. In this day and age, you don't live with the extended family, so the qualities of the person you marry are much more important than the family they come from. And BTs are often very fine people. You know they are people who seek good things in general, who are willing to change their lives. With FFBs, you don't know that at all.
But they don't want us. It's a stigma. It's a fear. It's just something different. Our accents are different and we speak English too well. It freaks them out.
And I wish I knew this because I wasted so much time on FFB women, wining and dining them. Sometimes they'd go out with me as much as 6 times. But every date felt like the first. They were just waiting for something to nix it because they never wanted a BT in the first place.
A few times, by the time I got to a BT, I was exhausted and sick of dating. Or I was busy with a FFB and couldn't date the BT.
My suggestion to BTs, focus on BTs. The odds are better of something working out. I'm not saying you can't marry an FFB. I'm just talking about probabilities of success.But be patient with them because they are changing over their lives and might just be a little on edge and a little confused. This doesn't mean they aren't worthy marriage partners.
I know a guy who won't date any woman who speaks BT-speak, ie sounds like she just came out of Neve. But that's not realistic. Because the other thing BTs need to be told is that they just went from having 50 million possible matches to about 50 or 5. You have to work with people and make your own success. It will not be handed to you.