"I do not understand why RDA cataloging examples and implementations have not picked up Bibframe as a prerequisite. They seem like not being made for each other, which is confusing and kind of bizarre.": I think the second point is answered earlier in the paragraph: "It is so simple that it even does not follow FRBR ..."
There are other reasons why RDA does not regard BIBFRAME as a prequisite:
It is not stable.
Its functional requirements are unclear.