There are legitimately much higher costs in shipping a pet than, say, the same weight in luggage. Why should passengers be subsidizing others people's pets?

I travel a lot, and I know what a huge burden it would be for me to have a pet, so I don't have one. I have drought-tolerant houseplants which can recover from a week going without water. Too many people have pets and then expect others to make unreasonable accommodations for them, when owning a pet is a choice that they made.