Why no AI memory?

I asked ChatGPT what it remembers about our dialog in last hour, day, week etc. the answer was this: “I don’t actually retain detailed memory of our past chats over time — so I can’t recall earlier conversations unless they’re visible right now in this thread.

If I had memory on, I could remember facts you asked me to keep (like preferences or ongoing projects) and bring them up later. But currently, I can only see what’s in this session.”

Is this true? If so why does chatGPT have no significant memory?