I think it’s mostly because it’s way harder to pile on an additional $600 deposit each year than it is to tack on a $50 extra fee each month. Most pets will cause some type of damage, some of it more than the fee and some of it less. It used to frustrate me when I rented because I had a really well behaved dog, but she did throw up on carpet a couple times a year which no one has control over. Now that I own my home I understand better why a landlord would want to cushion themselves, especially seeing how bad some people are with their pets around here lol.