It's because they're fundamentally a lot less concerned about killing people in the process. There's a reasonable debate to be had on whether the US is too concerned with the risk aspect of making progress on biotech.
That's rather flippant, and I'd like to provide a counterpoint. Some neuroscience researchers held a town hall discussion in a major US city and also in a major Chinese city (on two different occasions) about bioethics, and one of the topics discussed was whether it was morally right or wrong (in the case of IVF) to screen for IQ, assuming we had reliable markers. So, same parents, no edits, but out of N embryos, instead of randomly selecting one, you choose one that's likely to be the smartest. Assuming it works reliably, is that wrong?
The U.S. audience was split approx. 50/50, with most of the objections about how it was going against God's will, or that it was "unnatural." The Chinese audience was all for it, and expressed surprise that the U.S. audience was split. Because if you could, and the technique was reliable, why wouldn't you?
Sometimes, it's useful to take a second look at our cultural biases.
Annoying things I sometimes hear from relatives during family re-unions:
* Is it true that abortion isn't legal in the U.S.? (Of course, it's allowed, but not in all places, and ... it's complicated.)
* How come people don't understand that climate change is real? Is it because creationism is taught in schools? (Well, it's not like that in all places...)
* So did those comments from Trump become public before or after the election? People must have felt duped that they voted for this kind of person, right? (Actually, those came out before the election. I have no words. ::shakes head::)
Things I might ask them that are annoying:
* I thought gender-selection abortion is illegal. What's with the ratio? (Ugh. Country-people* and their backwards attitudes about gender. You'd think that top-down mandated equal-work-for-equal-pay for a generation would have changed a few things. At least city people have reasonable attitudes.) Yeah, so how are they able to do it? (Never underestimate what a determined Chinese person will figure out how to accomplish.)
* Wait, I thought country people expect their daughters to venture into manufacturing hubs to be breadwinners for the whole family? (Yeah, exactly. They totally baby the boys.)
(Country-people is the closest thing to a racial slur I've heard in China. The amount of prejudice I hear it uttered with me makes me quite uncomfortable.)
The point is that gender selective abortions are absolutely not legal in China. However, it is difficult to tell why you are aborting, and it is easy to look at your ultra sound pictures and tell.
(Anyways, our son is great despite me wanting a girl!)
The nongminren might have a different outlook, but in the cities girls are perfectly acceptable and welcomed.
https://www.nature.com/articles/nbt0104-3 (over a decade old)