I don’t think I’ve ever met a vegan who talked about it in contexts outside of organizing food for multiple people or in response to others asking about it.

I think it’s mostly that non-vegetarians (of whom I am one) know deep down that at least the vegetarians[1] are right and that they don’t like being reminded of their moral failings. Thus every time they plan getting food for a group and the vegans mention their culinary restrictions, they feel attacked and try to compensate for it by blaming the vegans.

[1] I’ve encountered to many people reporting that they experienced serious health issues with going full vegan, so I’m very much not convinced that veganism is something that works for everyone long term. The same issues do however clearly not apply to vegetarianism.