You can say that about any career. “If being a lawyer is such a good job, it will become saturated.” “If being a psychologist is such a good job, it will become saturated.” “If being a website developer is such a good job, it will become saturated.”
This is only true for the women’s fields, not the men’s and here’s why –
men’s talents are very limited so they can only go into fields they are good at. Women, on the other hand, can do anything, so if a field proves to be good for frum people, they grab it. that’s why the womens fields are all saturated (OT, Speech, nursing, ABA etc)
**snicker**
But since women only work at it part time…. it doubles the number of jobs available, so the jobs never saturate. (jk)
The serious answer is that many jobs have a barrier to entry, which keeps them relatively open. Actuarial science was mentioned, and is a good example as most people can’t pass the exams, not matter how hard they try. A doctor needs to go through the training, which takes many years. Even an accountant needs to pass exams, and work long hours during busy season.
Those jobs with lower barriers to entry (law with a BTL, nursing, OT/PT/Speech, computer graphics, etc.) do become saturated, and it is difficult for those who are not at the top (via product or schooling) to obtain positions, especially (from what I hear) in the NY/NJ area.