There's a pretty lengthy section in the middle of "What Technology Wants" by Kevin Kelly that argues against romanticized portraits of the hunter-gatherer lifestyle. Here's the short version:
Lifespans were short, so there were basically no old people. Old people are key carriers of institutional memory. Without them, you don't have much culture, and you can't learn from the past. Every generation is forced to reinvent the wheel. That's why they didn't develop technology or art.