Culture can be changed indeed, as can be seen in religion where branches has happened and whole demographics has gone and switched to different religions.

The reason for the decrease in smoking is still being researched and debate, but the main arguments that I have seen is the main role of smoking as social stress relief and as such it has been replaced by other addictions like opium use (mobile phone use, social media, and games has also been argued).

If we consider food culture to be malleable, we definitely should move to aquaculture as a main source of nutrients. Farms on land compete with forests and human activity, and land based farms uses artificial fertilizers (derived from natural gas) and massive amount of fresh water. Shellfish, invertebrates, and seaweed can provide both protein and calories, and has the lowest environmental impact of anything we eat today and can even have a positive environmental impact if farmed correctly. Changing farming from doing harm to doing good would have massive impact, and all it takes is a cultural change.

I think the difference is that smoking is also horrible for the smoker, and many want to quit, but can’t very easily. People don’t want to stop eating meat, driving their SUVs, buying cheap shit on Amazon, and flying to cool vacations. Stopping doing those things doesn’t benefit them unless everyone else stops too, and unlike smoking, we’ve made little progress in the last few decades (other than the progress unlocked by technology that means it’s immediately beneficial to the one making the change, like solar), so I can’t blame anyone for thinking that giving up meat to save the planet is stupid since their entire lifetime of lived experience tells them that the vast majority of their fellow humans are not going to do the same.

My washing machine doesn’t care how the electricity is produced, but most people can tell a vegan dish from a steak.

Energy policy is set by governments, which makes it a part of the political sphere

Veganism is an individual choice, and individual choices are generally pushed by culture

Of course culture and politics influence each other in a myriad of ways, but when people start to try and push individual choices like being vegan into the political space it is never very popular

I personally would fight tooth and nail to prevent veganism from becoming a law in my country. Failing that I would immediately make plans to move somewhere else.

That's not something most countries want