This is basically identical to the ChatGPT/GPT-3 situation ;) You know OpenAI themselves keep saying "we still don't understand why ChatGPT is so popular... GPT was already available via API for years!"
ChatGPT is quite different from GPT. Using GPT directly to have a nice dialogue simply doesn't work for most intents and purposes. Making it usable for a broad audience took quite some effort, including RLHF, which was not a trivial extension.