The ultra-orthodox are mostly all on welfare, paid a salary and given free housing by the Israeli government to study the Torah, which is probably not all that an essential activity, since it has been studied constantly for several thousand years. They have huge families, and their wives don't work. Then they retire at 60 and get a pension, also from the Israeli government. Most of their children also become Torah scholars and baby-making machines. It is clearly an unsustainable system.