I had shared your perspective but I think I moved off it a bit.
I think some of the lock/grappling moves have definitely escaped or have been lost to a significant segment of the karate crowd. Were these deliberately hidden? I really don't know. But, there are only so many ways that the body can move in an effective manner. Those core movements can translate into a variety of applications including striking, locking at grappling (I still think groundwork is significantly different though...)
Those core movements are the ABC's. The interpretations off those basics perhaps were taught fairly completely or left to the interpretation/improvisation of more advanced players, or a combination of both. Can't say.
What I do know is that in practicing the blade/stick arts -- another perspective -- is that I still see the core movements but varying levels of interpretation, from empty hand to edge, from blocking/parrying to locking and throwing. They are there. Some of the moves look like simple slashing, circular parrying, interesting stepping, etc. But, then seeing these moves interreted by advanced practitioners, I am given a view of "tying", disarming, locking, grappling, sweeping and throwing techniques. Still the same basic movements but more advanced interpretations.
I have always enjoyed watching your "jujutsu" interpretations of bunkai. I do think that each time, they are demonstrated, there is an opportunity of (re)integration of the locking/grappling possibilities in the Uechi system.