They are probably wearing a clean uniform and have spent several hours shining their boots. The last thing they want to do is climb under a house or into a hot, dirty, confined attic looking for a fleeing suspect who might be armed. Swat members are no different. They wear 20 to 30 pounds of gear plus, gas masks. The last place they want to be is under a house or in an attic.
Most dirty jobs go to the person who has the least seniority.
When a P.S.D. has been properly exposed to this type of search environment, he will drag you to any crawl space or tunnel he sees. They have no idea they can be seriously hurt or killed. To the dog, he is just playing a game of hide and seek. At the beginning, dogs do not naturally enjoy going under houses or into attics to search for suspects. When a dog is searching properly for a suspect, the dog will be in prey drive.