The law of supply and demand works regardless of what anyone attempts. Given that there is no shortage of candidates for jobs, it seems the wage is at a correct level. By comparison to college teachers, there is a tremendous oversupply of qualified applicants (sometimes hundreds of applicants for a single position), suggesting that their wages are too high. At present the supply and demand for teachers of Torah studies seems to be roughly at an equilibrium suggest the wages are neither too high nor too low.
One should note that teachers in Jewish schools get many benefits that make the low salaries more tolerable, such as being free from the discrimination anyone frum encounters working in the well-paid outside world. For most Torah teachers, switching to a better paying career would mean giving up much Yiddishkeit.