Nobody benefits from a missed appointment, except maybe the person that follows it (if they’re early enough). It is unlikely that a dentist will be able to fill a missed appointment by getting through each other patient quickly enough to add in any last-minute requests. Likewise, a missed appointment requires the patient to reschedule with a new date and time to keep track of, then make plans and accommodations to attend that appointment; they also still haven’t been able to see the dentist or get the planned work performed, which can lead to more problems.
Because of this, it is easy to think that business is business, and a dentist should do everything they can to take a late appointment. After all, the dentist will likely lose revenue equal to the appointment cost if they simply reschedule the appointment. This type of thinking can be argued for, yes; it can also be argued against, as pushing back subsequent appointments for the day to see a late arrival can cause those patients to get frustrated and leave or face their own scheduling conflicts. Basically, seeing a late patient, especially if that time commitment bites into other appointment slots, can cause the dentist’s other patients to experience the same type of discomfort the late patient was trying to avoid, which can cause the dentist to lose more than just their trust.