Are you vegan? Because honestly I think you're a bit naive about the public support for animal welfare. There are quite a lot of people who don't give a single shit about animal welfare. They're not the deciding factors when it comes to this kind of politics though. It's the farmers. Farmers are one of the strongest lobby groups in most countries and they oppose anything that hurts their bottom line. I'm from Israel, we have the highest percentage of vegans in the world and we had a big campaign a while ago to stop importing livestock (they would suffer a lot on the trip). The campaign failed.

I'm not saying that you can't find public support for some animal welfare policies, and many groups in the Effective Altruism space do work on that, but it's usually stuff like "hey maybe you can't keep this chicken in an individual cage where she literally can't move and instead put her in a cage with other chickens where she maybe will be able to take a few steps without stepping into another chicken". We're very far from like, banning slaughterhouses.