This belief people have that "beings kinda different to me" aren't suffering strikes me as near-far bias cranked up to 11.

That's surely a common reason, but are you sure you're not letting morally loaded annoyance at that phenomenon prejudice you against the proposition?

The cognitive differences between a human and a cow or a spider go far beyond "kinda", and, AFAIK, nobody really knows what "suffering" (in the sense we assign disutility to) is. Shared confusion creates room for reasonable disagreement over best guesses (though possibly not reasonable disagreement over how confused we are).

(See also.)