The story is that, for one reason or another, the architects of the modern synthesis had little or no understanding of cultural evolution. They failed to incorporate it into their synthesis. Then their synthesis became stagnant dogma, stifling innovation in the field.
I think that this story has considerable truth content, though obviously it isn't the whole story. A possible piece of evidence against the claim that the architects of the modern synthesis had little or no understanding of cultural evolution could potentially be found in the following books:
- Mankind Evolving by Theodosius Dobzhansky (1962)
- Human Culture and Evolution by Theodosius Dobzhansky and Ernest Boesiger (1983)
I haven't properly reviewed this evidence yet. Both books came out significantly after the modern synthesis crystallized, though.
Another problem with the thesis is that it doesn't offer an explanation for why the the architects of the modern synthesis lacked meme literacy in the first place. Maybe the explanation for that is sufficient to account for the lag, without the modern synthesis being to blame. I can't rule that out - but the modern synthesis was influential; it probably didn't help.
Looking at the memetics timeline the first half of the 20th century was an uneventful time for cultural evolution. In fact there are no entries at all from 1915 to 1945 - which is more-or-less when the modern synthesis came together. The founders of the modern synthesis were writing during a bleak time for cultural evolution. Perhaps the world wars were a factor here.