Ultra-Orthodox Judaism is not like the American religious practices you mention, where faith is a matter of identity but only expressed on Sundays or whatever. Ultra-Orthodox Judaism is a total way of life, for men especially it determines your daily schedule every day of the week. The Torah study that many men engage in full-time gives them a distinct body of knowledge and perspective that makes them feel part of the same culture as fellow ultra-Orthodox, while the secular world is an alien and potentially hostile place.
That isn’t to say that attrition doesn’t happen. It does. But this group has resisted it more than other faiths.
That isn’t to say that attrition doesn’t happen. It does. But this group has resisted it more than other faiths.