You're now talking nonsense just to try and support your weak analogy. This is not how a GPs works. It is not in the interest of the GP to double book patients. He gets paid a wage. It would suit him more to have patients not show up. Less work for the money. Also imagine if all the patients did show up, he'd be there till the following morning.
The reason you may wait is because patients do stay over the ten minutes and do talk about more than one issue. If you think you're late just think how late the GP is going home.
You also didn't specify GPs, you said doctors. To compare a doctor with a prossie is ludicrous.
GPs, or more specifically GP surgeries, get paid for how many patients they have on their books and the percentage of those patients whose problems are dealt with or referred up the ladder to the next guy. They also get paid for performing relevant tests so now everybody gets blood tests for everything. Google QOF. Perhaps an individual GP is paid on a salary basis, but the surgery won't earn money while nobody is being dealt with so they make sure that doesn't happen.
Any person whose job is essentially piece work is incentivised to not have downtime.
You cannot compare a doctor with a prossie.
This thread is about making a booking and the person not being available at that time - either cancelling you or making you wait. In that context I see a prossie as no different to a GP, a restaurant, a hairdresser etc. Probably the only real difference is WGs don't have waiting rooms and you don't always know their address so it's a lot easier to totally blank you if they gave your booking away.