"Yet the question that haunts me is 'WHY?' - Why do orgs exhibit various trends. I think the culture immune system is a good metaphor for the blue line."
From a (complexity-related) social emergence perspective, these various trends mean that "complex" systems (using communication processes as their coordination mechanisms)
have their own "dynamics".
In other words, such systems are beyond "external" control. They interpret attempts to control them / intervene in them, just as "perturbations".
And these perturbations are used depending on their own "structures"" (culture / values, mirco politics, decision mechanisms, org memory, etc.).
So, the specific dynamics of org communication processes would create those trends...