Because they’re the best at it!  This is cutting-edge technology in the war against the bed bug resurgence.   Bed bug trained canine inspector can detect eggs, nymphs and the bed bug infestations at an accuracy of > 95%.  A trained pest management professional’s accuracy rates <30% for bed bug infestations and < 1% for the eggs and nymphs.  University of Florida tests on bed bug dog s effectiveness.  http://bedbugger.com/2008/08/20/results-of-university-of-florida-tests-on-bed-bug-dog-effectiveness-are-out/
Because they are the best at it!
You can be confident that your canine inspector is motivated only by a love of treats and praise, not the contents of your wallet.  And bed bug inspections by dog are quick and simpler than those conducted by humans alone, because you won’t need to pull the carpet up and the furniture apart to find visible bed bugs, when the dog can tell you if they’re present by smell.
Bed bugs have a distinctive scent, and just as dogs can be trained to find explosives, illegal drugs, and people, they can also be made into bed bug finding experts.  Dogs are smaller and more flexible than people, so they can check those cracks, crevices, spaces in your furniture, and other areas that are hard for humans to access.  
Canine bed bug detection makes any necessary remediation easier and cheaper:  a dog can find a bed bug infestation while it is still limited to a small area, which limits the amount of money, work and time required to get rid of them for good.  It’s also safer for you, your customers or tenants, and the environment, because you can limit your use of pesticides.