Why it took (say) 9000 years to build the civilization that we have now? Did we need a major social change for example?
I wouldn't say that social changes where a big factor in the developement of technology. Some ancient cultures had more efficient social structures and more resources at their disposal than most nations nowadays.
I think the most simple explanation is that knowledge builds on itself. You can't develop the theory of general relativity if Newton wouldn't have provided the basic mechanics. And Newton couldn't have found them if he didn't have a whole lot of other data at his disposal, which again was developed by other data. I think the major tool for technological breakthroughs in the last century were electronics, which wouldn't have been possible without quantum physics, which wouldn't have been possible with a whole lot of other things.
The process could have been more optimised in retrospective, of course. For example, why didn't noone think of the rather simple mechanics of a printing press already a milenium before (which would have sped up further developement a lot).
But there are some connections that just can't be skiped. You can't split the atom without enough energy, so you need a coal powerplant. You can't have that without some significant advances in metalurgy, etc. etc.
Mad Max "what if" scenario: if we suddenly loose the ability of keeping the civilization in its current state by for example exploiting all oil without replacing it with alternatives, will we need additional 9000 years to rebuild everything? After all our brains didn't change much, so if we forget something / loose documentation, we need to redesign the wheel.
Suppose the atom wasn't split, we'd be running out of coal. FAST! once the coal is gone, where do you take the energy from to split the atom? I'd say if we'd have a major setback that would let us loose atomic power, earth wouldn't have the resources to allow for another go.