Many have pointed out on this thread that one of the reasons (if not the main reason) for the dumbing down has to do with a desire to appeal to the target audience. The org knows that its days of attracting the educated and well-read are over, so it's targeting the less educated and the less informed. Therefore, the literature is now designed so it will appeal to them and can be understood by them. I agree that that's a major reason, if not the main reason.
However, I still feel there are other reasons. For one, as I've already said, the org has to be more careful now. They've been busted too many times with their failed doctrine and prophecy. They know they can be torn to shreds by many educated, knowledgeable people if they venture into territory they once did in their literature. Also, as I've already mentioned, it's harder to get deeper, technical type material out now because it has to have the approval of too many individuals, not just one in the case of the Freddy days, and that many people won't all agree (Oubliette - I like your phrase - "doctine by committee"). Thirdly, as I've already mentioned, there is not enough brain power in the org. Somebody in an above post disagreed with that saying, for example, that the org has engineers, lawyers, etc. However, there are different kinds of smarts. One's being an engineer or lawyer does not necessarily mean he has the brain power and/or ability and/or talent to analyze somewhat obscure Bible passages with understanding and be able to effectively communicate his findings to others. I know some engineers and lawyers who are not very smart. Knorr was probably somewhat smart, but if he was, it was in a different way from Freddy. I don't think Knorr could have done what Freddy did; for one thing, I don't think he was as interested in it as Freddy was. (Just want to make it clear that I don't think Freddy was all that smart. He just had the passion and the interest and enough intelligence to appear at the time to be a guru.)
Believe me, I can tell from the org's writing that there ain't no smarts up there. I have vast lists of examples of their poor grammar, faulty logic, and just outright bad writing. I've even seen bad writing and bad grammar in material coming from the legal dept.
So I think there are a number of reasons, and the desire to appeal to the target audience may be the main one.