I didn't downvote you, but I will tell you what I think: probably because the comment is seen as irrelevant to the discussion, and also because people who don't care about human treatment of animals don't want to see comments about human treatment of animals.

First: the overall discussion is about where COVID-19 came from.

Second: this thread is discussing whether it's a natural mutation and subsequent transmission vs. somehow engineered by China. The OP made the comment that they don't understand why people are spending time looking at alternative theories because they believe it's assured that this came from a Chinese virology research lab.

Third: the comment parent to yours was a response to the OP saying the reason was because it fit the narrative of Mother Nature getting revenge on us for harming animals. This narrative was implied to be ridiculous; I suspect that most people in this thread do not believe 'Mother Nature' is an entity capable of taking deliberate actions like revenge. That comment was downvoted, probably because the commentariat here doesn't like sarcasm, but also maybe because they do not like to entertain nonsense. This kind of poisons the rest of the thread; here, there can be no legitimate meaningful followup comment to nonsense or in many cases sarcasm.

I think that your reply pointing out that we do mistreat animals ends up being seen as irrelevant and not contributing to the discussion. Whether or not we mistreat animals may be relevant to the 'Mother Nature' idea, but since that is seen as irrelevant to the actual discussion about COVID-19 origins, there's no point in posting the reply and thus the downvotes ensue.