[JudgePenitent]

Because there were so few people. The inverse of your question is why did technology seemingly explode beginning around 10k years ago? And the answer to that is simple: the Milankovitch cycles had brought about a warming trend, bringing an abundance of resources.

It is interesting to notice that sedentism and agriculture happened at the same time. The modern theory is that agriculture practice led to sedentism, but at the very least its unclear which came first because the earliest confirmed harvested (ie non wild growing) varieties of grains from the middle east come from approximately the same period as the beginning of this warming.

However, once not only agriculturalism but pastoralism (and even beyond that nomadic pastoralism, and the domestication of the horse) had proven their usefulness to maintaining scaling sedent populations, the populations exploded and naturally, bored human beings with brains and full bellies sit around and think of different ways to do things.

tl;dr: they were unlucky wrt technological innovation