You are aware even drs get sick and have to call out sometimes, right? Sometimes, there just isn't another Dr about to cover those appointments so the only possible solution is to reschedule. Maybe something more drastic happened to your doctor, like a death in their immediate family or they were injured in an accident, or any other thing that would impair their care to their patients.

It is annoying, to you as a patient with medical needs, absolutely. No doubt about it.

Either way, have some damn compassion or something. We're all perfectly flawed human beings.

On the other hand, if the rescheduling of appointments becomes a common thing, you can look around for a different doctor. Your wait time may be extended still.