For several years I have trained in lineage of Nobuyoshi Tamura. He often did very extensive aiki taiso (about 40 minutes). Never explained anything. I have also practised under Suganuma Sensei, same story. How can you expect your students (some of which eventually become teachers) to understand? It is like to them these exercises are common knowledge (i.e. know what they are for), while for 'us' they are not and are basically left in the dark.
Sometimes I think this intentional...
Maybe so - but maybe they DON'T know either because it was never explained to them as well