Two reasons. First, inspectors are physically inaccessible for most of the workday. You are in attics, on roofs, and inside crawlspaces where the phone is not reachable. Second, real estate transactions run on hard deadlines that do not allow for callbacks. A buyer with a Friday contingency needs an inspection on Wednesday and will call the next inspector if you do not pick up. The combination produces a higher leak rate than most trades face.