Teeth are also more intricate and "fiddly". Superficially arms legs fingers and toes are the same thing. Organic leverages. Their makeup due to evolution is advanced, but very straight to the point. They are also big. Teeth are small micro structures.

The major organs are all over the place. The heart and lungs oh so important, yet they be glorified pressure pumps nonetheless. The liver on the other hand, throw any shit into there and it magically outputs clear lifeforce for the body. Very interesting.

This is from a surgical point of view, as I view dentists also as surgeons in the mechanical regard. You have individual branches when you get into genetics/biology off each individual part, which is a whole different level off complexity.

The brain has neurologists, neuroscientist, psychiatrists and psychologists. Also very complex.

I think another reason might simply be the natural tendency to first tackle which lies in front. While genetics and such are interesting, people need direct help with broken limbs and failing organs, creating a pushing need for people requiring such skillsets. Teeth score the highest in this as well. If u break an arm it's w/e but teeth issues are often felt instantly and persist continuously if not dealt with.