Recent research from Cornell illustrates why modularity is fundamental to design including biological systems. Cost minimization in network systems naturally surfaces modularity as an important building block. This makes intuitive sense as modularity leads to complexity and ultimately intelligence.
Why, then, humans fail to consider modularity in the design of complex systems, systematically? Of course, every brick in the wall is expressed but not every wall in the city. Is modularity boring for those with intelligence or a mere convenience? Does modularity hide a regression from knowledge, or does it break new frontiers? Is modularity limiting or not? Does modularity evolve to an extent that it is able to obscure itself?
At the lowest level, one has to consider minimization of cost as the fundamental driver of modularity. The complication here is the definition of cost itself. First order societies, unable to feed, clothe and house their populations, may consider cost to be different among available alternatives in a limited choice set. Those who have gone further may define cost as ignorance, the minimization of which requires a break from modularity.
Nothing is for sure.