Why are some animal rescue groups so strict with potential adopters if they have so many animals that need homes?

I’m not talking about the home check or adoption application, I know it is necessary to make sure the animal is not going to some crazy person. I’m talking about extreme guidelines that may even discourage people from adopting. I just saw a rescue group who is trying to re home a dog but requires the adopter to have another animal who lives indoor, eats a raw diet, and the home must be a non smoking home. I got my dog from a rescue group and they didn’t have all these requirements and he has a very loving home.
Don’t these rescues realize that while they’re prolonging the process of adoption there are hundreds of dogs being put down in shelters every day? What encourages them to go beyond just a home check and have such strict guidelines for people who are just trying to add another pet to their families.