So as many other political movements around the world. A spark comes first, then maybe fire.
However, spark is just spark. Protesters of 6.4 was demanding something big, too big to be realistic. So they failed, paid high price for it.
To eat an elephant, you have to chop it into pieces first, then eat it piece by piece. Trying to eat an elephant in one sitting will probably kill the eater.
BTW: China is still opening up politically, it's slow but still opening. 20 years ago you wouldn't even imagine to be able sue the government for whatever they did, today however it's fairly common in some cases.
Economy I think is the main factor that force China to be more open. It's open up or die situation, I don't think even CCP had too many choice.