Well now you know. They are old schools that have survived due to certain practices, some are more relaxed than others but some are very strict in their entry and conduct requirements. Although "cult" is rather distasteful, in someways it's probably not far off. Koryu are specific institutions, organisations. As soon as someone says "this is koryu" then the question they will be asked is "which ryu?". A ryu is very specific, each one has it's own outlook, practices, traditions and even terminology. Koryu maybe an umbrella term but they are very rarely discussed in general terms because you are more often than not always talking about a specific school.