I suspect there's been some signal loss from when they were first taught. I've looked at some of the techniques I learned, and had to ask whether they were always this obscure and hard to get to, or have we (those learning the style) simply lost what the technique was supposed to be and/or what made it available (the entry or situation that makes it a reasonable choice).I think the portion in parenthesis really needs to be bolded. Some of the stuff passed down in the old days was complete bunk and never properly vetted or tested. Hence why I think our reverence for certain "relic" techniques and belief in their efficacy is misplaced.
I suspect some of both that and the never properly vetted. I also suspect there are some techniques that were meant for training a principle, rather than for application. They make great sense as drills, but not so much as functional fighting techniques.