They do marry other Jews or descendants of converts from other courts, they just don't marry converts or convert using their own courts. Therefore they are not a real endogamous population.
Also, the edict is only since 1937, they were accepting converts earlier than that. So fundamentally they aren't a success story - they haven't been doing this very long.
Other Jews can marry in, but even this is limited. The majority of self-identifying Jews in the US would not have the qualifications to marry in. Any how, they are an insular community.
Also, the edict is only since 1937, they were accepting converts earlier than that. So fundamentally they aren't a success story - they haven't been doing this very long.