1) Information Technology: It used to be that an idea would take months... years... decades to move across a continent or two. Now it takes seconds. Ideas move much faster, things change faster. Indeed, the ideas behind farming seem to have taken so long to take hold, thus changeing society from semi-nomadic hunter-gatherer-fishers to sedentry farmers, that Archaeologists now sometimes believe that farming was discovered in different places independantly, we're talking centuries here, perhaps even Milennia.
2) Population density. In the Mesolithic, there weren't many people. It is theorised that at some point in the Paleolithic humanity was reduced to less than 10,000 induviduals. Indeed, all modern humans are decended, genetically from only one of seven women. Though it isn't quite as simple as that. Ideas can only spread if there other people to spread them to. Simply, with no reason to innovate (no over-population, living in "Primitive Communism" in non-hierachical societies etc.) innovations were very few and far between. Innovations seem to come when they are needed or when someone might profit from them. Germany getting a bit too over-populated in the mid mesolithic? The canoe capable of a roll in water is invented, allowing the colonisation of scandinavia effectively.
3) Culture has changed: The roots of these changes go back to, in my opinion, the 16th century, in fact, 1517. The reformation and creation of protestant churches challenged how people thought about God. More, it gave political leaders power over the religious ones in a way which hadn't been true before. Once you start challenging the religious hierarchy it is the next logical step to start challenging the political one... and so on.
Of course it's never quite as simple as this and we could argue about minutae for hours, but it essentially boils down to IT, Ever increasing gobal population and deep-seated cultural change dating back centuries.
