Short Answer

The reason evolution-scientists had to resort to post-modernism and chaos theory is that it was a last-ditch effort to save the debunked hypothesis of evolution. Under post-modernism, there are no absolutes, so observation means nothing. Science is defined to mean whatever the evolution-scientists want it to mean. Under that form of lunacy, people can believe in evolution despite the obvious scientific facts.  Evolution isn't science.

Modernism had its beginnings around 1890. Under the original rules that the modernist-scientists set up, they started with the assumptions that there was no God, God did nothing, and no Creation or Flood. Then they set out to prove that there was no God, God did nothing, and no Creation or Flood. That seems like cheating, and it is insanity, but here is the kicker. By the 1970s, they had done enough experimentation to show that these rules, which they had termed “The Axioms of Science,” were absolutely false. That’s why they needed Post-Modernism and Chaos Theory so they could live in a make-believe world where there would be no absolutes, at least in their demented minds.

Detailed Answer

They really had it made. They set up the rules in such a way that they thought they couldn't possibly fail. Scientists really used to believe that they would be able to make up a bunch of stories, that would explain away all the inconsistencies between the theory of evolution and the things that they observed.

Think about it: they could lie as often as they liked, calling their lies, axioms. And they could keep adjusting their lies as more facts came to light. The only bondage they put themselves into was to say that they would end up with one set of rational-lie-zed speculations, those rational-lie-zed speculations would not conflict with the general idea of evolution, and would not conflict with any scientific observation, and would not conflict with each other. They could changes their rational-lie-zed speculations as often as they liked and they could change their theory as often as they liked. Then, they defined "proof of evolution" as being able to make up a set of uncheckable lies according to the rules just stated.

How could they fail?

They failed.

Somewhere in the seventies, it became obvious that they had gotten too much real information. They knew too much. Some realized it sooner than others. It was no longer possible to deny the existence of God. The most obvious and scientifically provable fact in all the universe became the reality of the Almighty and the fact that He created the earth. Without God, you can't have one set of rational-lie-zed speculations. No matter what you do, there is no way, given today's knowledge, that you can reconcile what is known to the notion that "There is no God." All of a sudden, the worldly liberals had to separate science into little boxes and make a different set of assumptions for each box. The more they learned, the more boxes they needed. It was getting out of hand. They had to subdivide their theories. They were starting to look very stupid. That made a lot of evolutionists very angry. What would they do!!? What would they do!!!?!

Then the answer came in a flash. The answer was so simple! How could they have missed it?

They would just say, there is no truth; no absolutes. That's when the Chaos Theory was born and Post Modernism came into being. Under chaos, anything can happen. Of course, you wouldn't be able to build houses or make cars using this theory, but it is very handy for fooling people. You can prove that darkness is light and that light is darkness. You can prove that there is no God. You can prove anything at all. It makes science absolutely irrelevant. It makes logic irrelevant.

Guess what? They're teaching post-modernism in the public schools. What a valuable learning experience for every student who wants to know how to be an idiot!

Rom 8:7  because the carnal mind is enmity against God, for it is not subject to the Law of God, neither indeed can it be.

Summary

Here is an amazing thing!
One of the most dogmatically held theories is the notion that there are no absolutes,
which is followed closely by the notion that no one can know anything,
which is followed closely by the notion that everyone is lying,
which is followed closely by the notion that the best liar wins,
which is followed closely by the desire to be the best liar,
which is followed closely by the destruction of a society.