Don’t know about cats, but can answer from dog perspective - I imagine it might apply to cats as well. And this is a completely utilitarian answer: food alergies. Animals can have them.

We have a dog who is alergic to most if not all most common meat proteins - chicken, pork, beef, fish… didn’t test all but you (and we) get the picture. Luckily, there are less common meat proteins (venison as one example) which he accepts just fine - but there was a distinct possibility he would not. So we would be faced with two options - buy him super expensive, ultra processed analergic food, or go for vegan options. If faced with this decision, I’d opt for option B for sure.

I know cats are seen as true carnivores and dogs are omnivores, but I think it applies to your question