Just a speculation and wild extrapolation, but what if NWO is not something they plan to implement, but something that is already implemented and has been for at least 100 years by now?
We can all see that most of what currently goes on in the world is engineered and orchestrated with specific goals to achieve. Covid scam goes without saying, of course, but the same could be said about current Ukraine/Russia situation, 9/11, Middle East, climate scam etc, etc.
So, what if most or even all recent historical events also were engineered? What if our historical narratives are simply lies and nothing much else?
For example, NWO could have started with WW1, which was engineered and implemented in order to get rid of Old World Order - old monarchies, dynasties, old wealth, old power and such. After it most of Europe was not monarchic anymore, but became national republics with supposedly democratic governments. Large multinational institutions were put in place. Again, supposedly to maintain peace, but in reality it essentially was One World Government in the making.
Then came WW2 which introduced severe limitations of freedom, a lot of new taxes and, most importantly, very simple and easy to understand narrative through which it was easy to control masses from all sides. Divide the world into good side and bad side. Nazis vs Allies during the war and Soviets vs West after the war. WW1 narrative was too messy and too hard to follow. Who fights whom? Why? Which coutry is on which side exactly? It was all too messy and unclear. WW2 hovewer was and still is presented as some kind of epic fight of good versus evil.
And now there's Phase 3 which started at the beginning of 2020 and is now being actively escalated in many various ways. After this phase NWO might come out in the open which up until now has been hiding behind various countries, organizations and such.
TL;DR: NWO already exists and all of 20th century events did not just happen out of the blue, but have been purposefully engineered and implemented with specific goals in mind. Most of official narratives, historical as well as current ones, are simply lies.
That's a good question.
One of the answers might be that their power is not absolute. They don't control every aspect of society, every aspect of economy and every aspect of politics. They do control the narrative, however, and the narrative is the main driving force behind modern society. Just look at past three years what the narrative can do. It does not matter if it's true or not. What matters is that it is percieved as true.
Another answer is that their plans also are not absolute. They do change and they do transform over time. Seems to me they work mostly on a kind of probing basis. They probe society and analyze what nonsense would fly and what wouldn't. Will the masses eat it up or wouldn't? Currently they are probing for things like insect diet, smart prison cities, UFO invasion and 1984 style infinite war.
And lastly all those good things you mention might have been useful for them at the time. For example, Western prosperity was very useful geopolitically as a counterweight to USSR. Look at them, they are poor, their economy is shit. Look at us, we are so, so much better than them! With all our freedoms and stuff! When USSR collapsed (probably intentionally) the image of prosperity and freedom was no longer relevant and currently we can all see the results of that. Of course they can't take away all the freedom and wealth in one day, but they are working on that. Oh, they are!
EDIT: Regarding population numbers. How do you know that those are real population numbers? How do you know that our population is indeed balooning? Oh, from Wikipedia? But we all know that Wikipedia is one of the biggest narrative peddlers. So, here you are. Our population might be even smaller than it was, say, 100 years ago. Our climate might even be in a better shape than it was 100 years ago. It's the narrative that matters. Not facts or reality. We simply do not know what the real reality is.