Why it happened is not nearly as important as what it unveiled: that versioned immutable systems are the most powerful system design concept in history. Most people have not yet grasped what an insanely powerful concept it is. At some point in the future, maybe 50-100 years from now, someone will look back and say "holy shit; deploying web apps are where this concept came from?" I hope in my lifetime that people get it and start applying it to other system designs/components.