Why is it becoming increasingly more wrong to kill animals for food?

Probably in the majority of history people used to hunt, or kill farm animals for food without a second thought. But in the recent years it looks like the public opinion is shifting in a way when perception of eating meat is kinda like perception of homophobia or racism. Arguments against eating meat and for preserving farm animal lives are actively upvoted, and with this tendency being non vegetarian is already becoming "uncool" and eventually will be frowned upon, like littering.

Is that because hardcore vegetarians and animal rights activists got their voices spread in social media? Or it's mostly an environmental problem, particularly with large farm animals? Or humans are quickly becoming better, more civilized? If so, why meat eating is such a high priority issue to address when issues of people to people interactions are still far from being solved?