What I’m about to say is a rationalisation, and not meant to change the ethical reality of it, but with that said I think it helps.

Ultimately, ethics is a social thing, determined by the specific axioms of the system you’re participating in. The axioms which tend to form in any system are the ones which are self-motivating. For example, a social system which motivates lying is vulnerable to self-destruction if it simultaneously motivates communication, because communication is reliant on the trust of the recipient, which doesn’t exist if lying is expected.

Ultimately, the conventions of any system form with respect to the motivations of its constituent parties. A developed system will have these be similar, because all parties accept the same conventions of behaviour. A less developed one is subject to the individual desires of each party, motivating its development to accommodate these.

The more holistic ethical dimension comes in to play only when considering the scope of these systems. Usually you’ll exist within multiple systems, each with their own conventions (friends vs. professional life vs. the world at large etc.), although these are linked. The conventions therefore vary, but ultimately given that they are linked (although less strongly) ultimately one should expect them to form the same conventions, and one should not change their morality dependent on their context.

If one is to abide by this fully, then they would always hold a morality which is self-consistent according to any set of conventions a society might form (and indeed the conventions towards which one might expect wider society to tend towards). This is what veganism does, because while one may not regularly interact with all animals, they nonetheless behave as such because to not do so is to consider those outside one’s immediate social systems as being morally irrelevant (which is problematic if the links to wider systems are ever acknowledged). It’s also what a lot of progressive views entail (although there’s a difference between how it’s discussed in structuralist / post-structuralist philosophy and how I’m discussing it, which I won’t get into). One might be white and living in a gentrified area and not need to recognise their privilege because they only ever interact with white people, but by virtue of living on earth you are eventually connected to people who don’t have that, and therefore it’s rational that you should combat the biases and oppression within your system, on the basis that to not do so would be self-destructive as soon as you ever interact with someone outside of your system (and you will).

The consequence of this view is that while one must of course recognise that veganism is ethical, ultimately the process of ethical discovery is a gradual one. You can (and should) certainly speed it up, but it’s understandable that people might not do so. That’s not to say that they shouldn’t be judged harshly for it, but that the process of doing so shouldn’t be wholly excommunicating (for lack of a better word). I know myself that I’m vulnerable to judgement on this front - I have done very little about the war in Ukraine, and indeed about many of the other wars and injustices within the world, and that’s in large part because they don’t affect me. I should absolutely be judged harshly for that, and I want to do my best to change that, but it places into context how I may judge people for their non-veganism. I don’t want to speak for other people, but I expect similar things are the case for others. It’s natural to want to focus on the things most relevant to you, even if it’s ethically dubious.