In short, we've become so innovative because collectively we've created a global environment which facilitates creativity.
Innovation appears in environments that resemble a liquid environment. A habitat in which ideas can flow freely through the network and combine, merge, connect in many unpredictable ways.
Historically, we were closer and further away from creating such a habitat.
Hunter-gatherers had an environment similar to a gas state. Groups of at most hundreds of people lived separated from each other in their pockets of existence. For that reason, the ideas rarely interchanged and connected, which made innovation impossible.
In antiquity, thousands of people started occupying a shared space and sharing a common culture. This situation led to information spillover. The process when numerous ideas flow from person to person, even if these ideas are being tried to keep secret. The pinnacle of this condition was ancient Rome (which some say was surprisingly close to having an industrial revolution).
However, the middle ages changed this situation. The feudal system was a hierarchical system where power (and knowledge) were passed down from the top and strictly controlled. This situation prevented ideas from freely flowing through the system, which stopped innovation. This environment resembled a solid.
During the renaissance, castles were replaced by market places. Ideas became less hierarchical and more networked. The number of possible connections in a market greatly exceeded the amount that was possible in a castle. It allowed ideas to circulate freely through a wider connected population. It allowed information spillover to happen - it became liquid.
Further down the road, with some bumps on the way, our environment was becoming more liquid. Mass communication enabled communication without physical contact which further increased the collective pot in which ideas could mix. The internet was another massive milestone in creativity as it democratized information creating a somewhat collective brain.
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