People consider vegans on Lemmy as too preachy. Even in vegan communities here, mods have to remove soooo many inappropriate comments (I read a few of these and they keep getting removed for good reasons). Comments that suggest going vegan on posts about animal abuse are downvoted.
At the same time, whenever there is something about Windows or Chromium based browsers, people here are doing exactly the same. “Just use Linux/Firefox/whatever”.
It’s not my experience that anyone mentioning veganism ends with a negative score.
How do you know you’re not just encountering sampling error? Maybe you’re in different communities than where I’m seeing veganism discussed.