A lot of the reasons to stay in America are personal.
* Compared to my in-laws in Japan, my parents here in the US are younger, more able, and far more supportive in general. We're getting way more help with our kids here than we would in Japan. We're getting more financial support. It's difficult to admit but it's a very simple truth.
* I have an older brother on the autistic spectrum who greatly benefits from having me nearby. And I'd probably need to take up his care if something happened to my parents, so it makes sense to be settled in the US.
* Our kids are biracial. Their social lives would probably be more difficult in Japan. Meanwhile, that's almost the norm where we live in California.
* My career prospects are far more open in the US. You definitely feel the "gaijin glass ceiling" when you're working in a Japanese company. This may be changing today. But it was very true back in the mid-00s.
* Likewise, my wife's career prospects are more promising in the US too. It's very difficult to get a salaried, high-paying job in Japan, especially as a woman, and especially as a person reentering the job market in middle age. That's not easy in America either, but not impossible like Japan. It would be a massive shame for her mind and education to go to waste. Japanese society is fucking this up badly.
* Today's Japan does not smile upon children. If you take your kids to a restaurant, or take them on the train, or really try to do anything with them in public, then grit your teeth. You're going to be surrounded by old people everywhere, and many will be shooting you evil glares. To simply have kids is to disrupt the harmony. I've literally seen public parks get shut down because old people living across the street couldn't tolerate the sound of kids laughing. This isn't specific to my having half-breed kids; I hear the same from almost everyone. We actually know a lot of Japanese families (several dozen) who are staying in America mostly for this reason, planning to go back after their kids grow up.
I loved living in Japan as an unencumbered young person. There are many things that Japan gets really right, like big city life, that's almost universally terrible in the US. When we go visit Japan, we come back kind of disgusted by America: there's trash everywhere, food is gross, certain neighborhoods are unsafe, every other person is obese, etc. Still, considering the above, the scales tip in favor of the US for us.