I’ve seen plenty of dogs and cats that were long past their quality of life.
OK, but that's not what people are arguing with you about. I don't think people would disagree with you if you were only talking about spending money on pets to extend their lives without making them happy/comfortable. But there are a lot of instances where you can increase your pets lifespan without losing any quality of life. Sometimes that's expensive, and it can be a really hard choice to make (especially if you have trouble affording it), but it sounds like you're arguing that people shouldn't spend a lot of money on their pets no matter what. That's absurd.
If you really love your cat, why do you think it's wrong to spend money to prolong her life? Assuming it doesn't involve suffering on her part, of course.
I feed her. That's the maximum expenditure. Not even yearly visits to the vet. She's an animal. There are countless other cats/kittens at any given moment.
People are straight up nutso to make it a bigger issue.