I think the idea is that the other creatures, like animals bred in captivity for their meat, are the ones which aren't protected. Vegans don't seem to speak for them (as say, a liberal might for a marginalized group while denying them their voice) rather use inductive reasoning to reflect contradictions in meat-eaters and their ethics in practice, particularly around ideas of self-oriented material interest.

If we use genocide as the mass slaughter of any life (we'll probably conveniently ignore microbes and only stick with multicellular life) rather than human life, animals bred for consumption (as well as those affected by humanity's effect on the environment) are deliberately genocided and it's done to some anticipation. The scale makes this far worse, other humans can be a meaningful threat and thus for the oppressor it is reasonable to eliminate them if their very existence poses a threat, as is the case in settler-colonial societies.

I don't know why you or others might treat non-human life differently than human life, and that is what I consider to be occurring. Feel free to disagree, I would be curious to read your thoughts as it's not a perspective I would say I understand. Three reasons for my prior comment which come to mind are 1. anthropocentrism, 2. lack of empathy and 3. solipsism. For the second there is a relevant quote which I think captures this well:

"In my work with the defendants (at the Nuremberg Trails 1945-1949) I was searching for the nature of evil and I now think I have come close to defining it. A lack of empathy. It’s the one characteristic that connects all the defendants, a genuine incapacity to feel with their fellow men. Evil, I think, is the absence of empathy." — G. M. Gilbert

If instead of 'fellow men' you put 'fellow creature' I think you might understand where some of the arguments come from. Don't get me started on eugenics and how we are more or less perfecting it with plants and domesticated animals.