im pretty sure one of the main reasons systems thinking is unpopular is because Robert McNamara applied it to the Vietnam War and it didn't work.
McNamara was too much of a nerd in the inability to apply real-world critical thinking. He probably looked for a wife using a punchcard program in FORTRAN on an IBM mainframe. Hell, he looked more IBM than IBMers. Combined with the unpopularity of the war, all fruits of his efforts were poisoned.
If, say, Ross Perot had been SECDEF, perhaps the war would've ended sooner and the MIC wouldn't have been handed as much money, and possibly could've introduced McKinsey-like thinking.