Just watched for the first time
Just watched this film film, and I have an idea to the point.
Bubby is a clean slate to bounce millennium old cliches off of. These aspects of society he is subjected to are the age old and timeless. Bubby in his complete abject ignorance is somehow able to cut and paste witticisms and cliches in to an actual philosophy.
His parroting of sentences is an example of how the general populace just spout senseless "logic" with out truly thinking of the meaning behind it. People simply repeat what they're taught with out truly understanding the significance because it's all been said before, it's accepted as a universal truth.
Bubby doesn't have that, so each of these witticisms he hears is true genius to be pondered. He is able to copy and paste them in real life to make his thoughts known.
I think the real message is to not take what we experience in life for granted just because it's the "norm". Regardless of how old the message is, there's always something to be learned and applied. Even if you're a 30-something, mentally disabled, matricidal/parricidal, incestuous, individual.