Reactionary thought (or ideology generally) isn’t heritable. Most of these people treat their children like shit, and while that doesn’t mean they’ll turn into leftists, it does mean that the children of reactionaries are far from certain to become reactionaries themselves. This is especially true for “normal” chuds, who still want to be participants in mainstream society and politically engaged. Mennonites have a high retention rate in part because they’re disengaged from normal society and they provide a supportive, insular community. Most chuds just treat their kids like shit, and also don’t provide any kind of integrated, supportive community. That’s a (materialist) recipe for losing converts.