China doesn't really care about the environment. Their top priority is growth in order to avoid social unrest, and for feeding all the people they need all the food they can get - and if antibiotics makes farming more productive, they'll do it.
The US, on the other hand, has the problem that Big Ag is a powerful lobby. And Trump, given his total lack of understanding on climate and environmental issues, won't do anything to change that.
This is how every rich country went through industrialization. Not because they were all immoral, but because they were poor.
The good news is that China is somehow doing this in fast forward. Each Chinese year seems to be 3 years in a regular economy, and their enormous push for solar power is (I hope) just one sign of what's to come.
Percentage-wise?
https://en.wikipedia.org/wiki/Jevons's_paradox is the same basic idea.
Meat demand as price drops may end up in pet food or 'corn' flakes, but the usage does not really matter. In competitive markets producers tend to make a fixed percentage of sales as profits. Thus, increasing total sales tends to also increase industry profits.