Almost all people almost never have truly original ideas. When asked to "tell me an idea [you] have never heard before", they will remix stuff they have heard to get something that "feels" like it's new. In some cases they'll actually be wrong and reproduce something they heard and forgot about hearing, but remember the concept. Most of the time, the remix will be fairly superficial.

And remixing stuff it has heard before is exactly what ChatGPT is doing. What it sucks at is the "feels like it's new" part, but fundamentally it would be quite easily capable of creating output that combines concepts with maximally negative correlation, the only thing that's truly missing is the ability to interpret the prompt as an instruction to do that.