[nitwit005]

The inventions we care about today are only useful to a certain sort of society, and it took a long time for that to emerge.

Imagine you're in a jungle with your tribe. You basically have plants, animals and rocks with which to make stuff. You live marginally, and people sometimes die from starvation. Your tribe migrates, meaning you have to carry everything you need with you.

If you happened to figure out some metal working, it's probably not worth doing. Your tribe can't set up a mine, and gathering fuel is a huge effort.

Realistically, that sort of thing probably needs an agricultural society that can afford to feed people who aren't farmers.