I've talked to many non-vegan leftists and they are the most puzzling type of person to me.
Like how are they even justifying participating in animal torture to themselves? All the things they critique about the brutality of capitalism could be applied them just easily! Somehow most of them seem incapable of entertaining the thought that perhaps actively and willfully engaging in the practices they themselves deem morally reprehensible is not the best course of action (gasp!) .
Every time I try to reason with them they pull same straw-grasping bullshit as liberals desperately trying to hold on to their unjustifiable beliefs -- it's the same arguments from them every time too:
"no ethical comsumption under capitalism"
"not everybody can be vegan"
"unsustainable diet"
Do they seriously not see the hypocrisy or are they actually incapable of making a small sacrifice of their own happiness for the good of animals‽
It's mostly the fact that individual lifestyle choices won't do anything (no ethical consumption under capitalism, etc).
Widespread veganism will never occur under capitalism, there's too much profit motive in the meat industry. As long as capitalists can exploit that industry, it's going to be there. Individual choices will not affect anything in a systemic way, being vegan is simply a personal choice that makes someone feel better. Same way that choosing one seller over another because it may be more "ethical" but won't push for any systemic change, or trying to lower your carbon footprint won't do anything for society as the onus of climate change is on capitalist producers and industrialization.
Side note, I've also noticed that while most communist vegans understand this, liberal vegans tend to be the stereotype of the over-the-top vegan who get stereotyped as pushing views down peoples' throats. They don't approach things materially, it's the liberal thinking that individuality and ideas change material condition instead of the other way around.