I think it's more that fixing teeth is largely about replicating a specific material with one-off procedures, whereas fixing hair is all about controlling a complex never-ending process that is linked to all sorts of factors.
Also, everyone has teeth issues, whereas hair issues are mostly limited to a subsection of the population (older males, and not even all of them).
> subsection of the population (older males, and not even all of them)
Those men will pay lot of money to get back their hair though.
If I not mistaken it was Bill Gates who said more money is spent in hair regrowth research compared to vaccine to prevent diseases like malaria which kills thousand of people.
Also, everyone has teeth issues, whereas hair issues are mostly limited to a subsection of the population (older males, and not even all of them).