Your question doesn't make much sense, probably it would if we reframe it as why don't people use chatgpt instead of some wrapper. Answer is because it is just a simple chat interface and many applications go beyond that.
One good reason is that 99.9% of the world population does not own a computer powerful enough to inference ChatGPT or GPT-4.
can't i just use chat.openai.com ?
Oh, for sure. That's what I do; I don't use ChatGPT enough to pay for an API key. I misunderstood your question.
Why do people use CRUD database wrappers instead of using databases directly?