Predictability is the inverse of information density.
Low information density enables high compression, and vice versa.
It's called entropy. This is basic information theory to be quite frank..
Because most of the training data has good grammar, the LLM is strongly trained on grammar; it will rarely predict ungrammatical gibberish. Even if there are grammar mistakes in the data, they are not systematic and so don't reinforce each other.
2) if 1) then "prediction" isn't the word I'm looking at.
LLM embeddings are compressed training data.
To decompress that is to make a prediction (in this case to convert the embedding into readable text)
I’m starting to think that compression is not, in fact, prediction.