They probably spoke with their lawyers and realized they have little to be scared about.
1. They may be offering already additional time then the right-wing Yeshiva’s do for secular education. So they might be meeting the requirements as is, and even if not, the amount off would likely not be much.
2. Their academic performance levels by all measures (regents, SAT scores, acceptance to college, etc) often place them in the top schools in the State
3. Very few students after graduating ever have to apply for welfare and they are overall self-sufficient.
Taken together, the State would have a very difficult time arguing with them how to educate. Freedom of religion does apply and if the State can’t point to any reason, other then an arbitrary set of guidelines, then the State will likely lose in court if they tried forcing them to do much.
Contrast this to the right-wing Yeshiva’s (especially the few that don’t teach any secular education… the Satmar Rebbe in a recent address, openly said this about his schools).
1. Secular studies is limited to 4 days a week, for 90 minutes to a few hours (depending on the specific school and assuming they actually teach secular studies).
2. Due to lack of secular education, some of the more extreme schools have no academic performance levels to assess them by or they are minimally relevant (e.g. is everyone taking regents, what about the kids who don’t show up to secular studies?)
3. With numerous students in Kollel, even from schools that academics are decent, they still rely heavily on social welfare and many are not self-sufficient. From schools with no secular studies, the amount of people on social welfare are seemingly from the highest levels out there (look at data for New Square, Kiryas Joel, and Yiddish Williamsburg).
On point 3 alone, which is kind of a big deal, the State can justify that since outcomes are not good they have a right to regulate. So Yeshiva’s have much greater reason to be concerned.
Some might argue that the reasons for social welfare are larger families, etc. It really does not matter the reason. Consider a thought exercise. If everyone in the country did exactly what these Yeshiva’s do, then the rate of people on welfare in this country would shoot up and very likely create an unsustainable situation. Hence, even if this is relatively a small part of the overall population it is not a good outcome. I am sure a smart person here could argue my analysis is wrong. It really does not matter. The burden of showing that Yeshiva’s produce good outcomes, is going to rest much heavier on the Yeshivas then on the State. So unless you have very clear and powerful arguments to bring to a judge, the State will very likely be found to have a clear right to regulate. As to the specifics of how to regulate, that might be up for debate.