He's a professional. He genuinely cares about your dental health. Most medical doctors enter the profession because they genuinely want to help people, not exploit them for bucks. And prevention is very often the best method of help.

Compare him to the programmer who creates an extensible open framework, as opposed to the guy who throws together a dense hack that only he understands. The latter could be said to be acting more in his own interest, but the former is more dedicated to his profession and the greater good.

Every time my dental hygienist asks whether or not I'm flossing regularly, I reply that if they can't already tell the answer by looking closely then there's no point in flossing!

When you neglect to care for your teeth, you probably neglect to have others care for them as well. I'll bet the dentists' best patients are the OCD types who brush and floss five times a day.

Maybe if more people floss their teeth, cleanings would go faster, allowing him to see more patients, partially making up for the scarcity of expensive dental procedures?

Short term, yes.

Longer term, not so much. As word gets around that he isn't a good dentist, he will have fewer customers.

You found it a bit odd that he's not cynical?