Sounds like you’re suggesting that teachers work longer hours for no additional compensation. That is unacceptable, and if someone suggested that for whatever industry you’re in (i.e. computer programmers across the board be put to work another 5 hours a week at their current pay) you’d have close to a revolt and it wouldn’t fly.
Rebbeim are already paid less than most other professions as it is, while almost singlehandedly ensuring the future of our most precious gift — our children.