Why this is, I'm not sure. Perhaps it has to do with the fact that both Whites and Asians do well academically and economically, and so they're socializing more in school and in the workplace. That's how my older brother met his Asian wife (she's originally from Hong Kong). My older brother attended UC Berkeley, which is dominated by Asian students.
Further proof of the socioeconomic-driven explanation for interracial relationships is the demographic profiles of the White women that are dating black men. They tend to be overweight, poorly educated, and impoverished. So, again, contrary to your beliefs, it's the undesirable White women that are struggling to find a White male partner, and so they're settling for the black male chubby chasers.

If the statistics from these studies tell us anything, it's that it's White men that are betraying their race by chasing after non-White women. So, rather than focusing on condemning White women for being traitors to their race, we should instead be denouncing White men for dating non-White women.

Better still, we should be kicking non-Whites out of our countries so that we don't have to worry about this problem. Not a day goes by that I don't feel genuine hatred towards my older brother for settling down with a freaking mongoloid. He was a stud. He's 6'4", athletic, handsome, charming, intelligent, and rich. He could have had a super hot White trophy wife. Instead I have to pretend to like his wife and my weird looking hapa niece and nephew.