Because one depends on these dogs for one's freedom and even life.
Extra care must be taken in their care, feeding and housing.
Fences must be carefully maintained not just to keep the SD in but to keep other dogs out and humans who might want to get to the working dog.
One has to take fewer risks with a SD because to replace one is difficult and can take a lot of time to find another one.
Off leash dogs parks can be a hazard for a working service dog's career as a working dog, when with a pet it would be an acceptable risk.
One has to be careful on their food and to feed a good quality food. This is to avoid things which could hurt their ability to work or shorten their working life. So one must keep their nutritional needs in mind because they have a higher stress job than a pet does. As they get older one must often give good quality supplements to keep them healthy longer and able to keep working.
Small injuries and even minor illnesses can knock a dog out of being able to work in public. So they often have to get more vet care when a minor things comes up so it does not become a major thing which could end their career. A cut on a pet dog's foot is no big deal but on a service dog can put them out of being able to work for some time.
Waiting on a health issue is not an option when you depend on this dog for being able to do daily activities and get out and about in the community.
Screening for health issues like hips, elbows, eyes, thyroid and other breed specific issues are needed to make sure the dog is fit for continued working. Some need to be rescreened as they get older for possible issues with arthritis or other things which may tell the owner when they need to start looking for a replacement.
In a pet this would be rarely done unless an animal was being considered for breeding.
These are just some of the things which make owning a service dog more costly than having just a house or yard pet.
Not to mention the cost of equipment can add to the cost of having a SD also .
