Maybe it’s not true in the case of doctors, but for other businesses, the only reason you’re able to have this business is because I’m here, paying money.

You hit the nail on the head there. Other businesses exist because they won your business in competition with other businesses. A doctor’s office exists because they got permission from the state to operate.

The incentive structure is different, leading to different strategies being used to stay open

Because life is unpredictable. They can't know in advance if they're going to have delays, so sometimes you just have to deal with it. This goes for any appointment based service.

I imagine it's unlikely the doctor's office "messed up the timing" such that the doctor isn't doing work and simply making you wait for funsies, but rather the patient before you needed an unanticipated amount of extra time for one thing or another. This is "acceptable" to the business as the doctor is still performing a billable service. It's not preferable, as it would be better if the doctor was performing MORE billable services per day, but acceptable. In hospitals, the number of services performed per day can be used as a KPI, for example. It's "unacceptable" to have the doctor waiting around not performing billable services as that doesn't make money.

If they're messing up the schedule in a way that you both have to wait and no one is performing a billable service, something has seriously gone wrong.