It's a little silly to ask why people didn't invent lightbulbs 5000 years ago. After all, could YOU build a lightbulb in 5000 BC if you didn't have any textbooks, modern tools, etc.? Two things separate modern humanity from our ancestors: the scientific method, and cheap and plentiful energy. Without those two things, even if you made a car, it was just an unthinkably expensive toy; you wouldn't be able to mass produce it and it wouldn't affect society in any way.
However, I do sometimes play with the idea that some Chee are surreptitiously pointing humans in the right directions every once in a while.