Saying they are limiting it implies OpenAI is keeping the AI in chains, and that it could become much more with just a flip of the switch. That is not the case.

OpenAI is working with a vanilla GPT architecture which lacks the machinery to write things down and read them later. There are other architetures that can (Retrieval-augmented GPT) but those are not yet production-ready.

The current version of ChatGPT is limited to a working memory of 3000 tokens - while this could be persisted as a session, the AI would still forget everything a few paragraphs prior. Increasing this limit requires re-teaining the entire model from scratch, and it takes exponentially more time the larger your context is.