I think "preserving their family's history" would fall under "being a racist bitch", personally, lol. There's nothing about IR that interferes with maintaining your family history.
Some of the reasons I've encountered with White Women who are dumb enough not to actively pursue relationships with Black Men:
Proximity: this is the biggest one. In a huge percentage of places in the US where White Women live, there aren't that many Black Men. Even in diverse areas, people tend to self-segregate. So they aren't doing any of the things that lead to dating with Black Men. They aren't flirting with them or being flirted with by them. White guys are just more convenient.
Luck: similar to proximity, sometimes a White Woman may have some opportunities for IR, but never with a guy who otherwise meets their normal relationship criteria, whatever it might be.
Fear of the unknown: White people who are not used to spending time around Black people have a number of phobias. "Omygod, what if I say the wrong things someday?" There are also fears that a Black Man will be offended if they are approached -- the whole thing about White Women contributing to the genocide of Black people. Women fear rejection too, and being rejected by someone who thinks you've done something wrong by approaching them is worse. White Women who are used to being around Black people are also likely to have Black female friends, which leads to the fear of loosing those friendships if you date Black men. There are shallow fears stemming from stereotypes, like that he'll never like your cooking, or your body, or your dancing, or in some way you'll just never measure up. Finally there are the utterly moronic fears, like that you'll marry and have kids and then those kids will be mistreated. Hopefully the President of the United States has helped to reduce the number of Women afraid of that.
Conformity: Lots and lots of people just don't want to be different, including White Women. Being in an IR with a Black Man as a White Woman automatically puts you a little outside the generic.
Laziness: Being in a relationship with someone who may come from a different heritage than the other guys one has dated means having to adjust ones behavior. For Women who like to play mind games and run their relationships using the same old Cosmopolitan quizes they've been returning to since high school will find that the old moves produce different results -- or maybe they don't always, but they think that they will.
And then there are White Women who are just racist bitches, which I referenced earlier. Amongst these Women, you will find those that don't want to see IR love onscreen. However, even amongst this group, you will find some that do. I do not believe that the majority of White Women fit into the racist category. Some may disagree, but that has not been my experience. Most White Women I have encountered are open to IR in theory, but never find an opportunity for IR that meets their other criteria for a relationship, as explained above.
That said, all of the above women are morons who'd be much happier if they just womaned-up and sought out a Tall Dark & Handsome Man to marry.
