The rarity of personal fitness enthusiast PE teachers in public ed is mostly due to defunding, especially in places like the US. They do exist (and are effectively donating their time, because they’re enthusiasts) but the typical “PE teacher” is more like a longterm substitute whose qualifications are limited to playing a sport in their teenage years.

IME you can tell when a school has no real PE teachers by how many male teachers at the school call each other “coach.”