I'm not sure there was a "cause," per se, but evidently a population stumbled on a winning formula that made them and their descendents much more fit than other hominin populations. Think of it as analogous to the discovery of iron, 3000 years ago: populations that had iron in a very short time were able to overrun every population in Eurasia that didn't have iron.
Another part of it is a population question -- these more advanced hunter/gather societies were able to support far larger populations that essentialy swamped what had been there before.
There is documented, gradual evolution in tool technologies leading up to this explosion, but if you're asking what the key turning point was, I don't know.
All tools develop according to need; the more hostile the environment, the greater the need for tools.
Now we're in the age of toys.