One explanation is that they were never that good in the first place. This is highly plausible as our brain has no reason to be optimized for high quality thoughts. However, another possibility is that the process of translating the idea into language somehow distorts it. It could be that one lacks the vocabulary, there isn’t a word that matches the idea, or one simply isn’t articulate enough. It could also be that language is a poor descriptor for our abstract conception of reality. Could there be ideas or concepts that language could not express? Such ideas are likely impossible or at least incredibly difficult to communicate. There are certainly ideas that language has a hard time communicating in a literal sense. Often, narrative is used to attempt to communicate these ideas. And it at least feels like there are ideas in narratives that aren’t fully expressible in simpler language.