“The Big Five came along at a perfect time to roll up the user base,” said Geoffrey G. Parker, a business professor at Tulane University and the co-author of “Platform Revolution,” a forthcoming book that explains some of the reasons these businesses may continue their dominance. “These five rode that perfect wave of technological change — an incredible decrease in the cost of I.T., much more network connectivity and the rise of mobile phones. Those three things came together, and there they were, perfectly poised to grow and take advantage of the change.”

Mr. Parker notes the Big Five’s power does not necessarily prevent newer tech companies from becoming huge. Uber might upend the transportation industry, Airbnb could rule hospitality and, as I argued last week, Netflix is bent on consuming the entertainment business. But if such new giants do come along, they’re likely to stand alongside today’s Big Five, not replace them.

Indeed, the Frightful Five are so well protected against start-ups that in most situations, the rise of new companies only solidifies their lead.

Consider that Netflix hosts its movies on Amazon’s cloud, and Google’s venture capital arm has a huge investment in Uber. Or consider all the in-app payments that Apple and Google get from their app stores, and all the marketing dollars that Google and Facebook reap from start-ups looking to get you to download their stuff.

This gets to the core of the Frightful Five’s indomitability. They have each built several enormous technologies that are central to just about everything we do with computers. In tech jargon, they own many of the world’s most valuable “platforms” — the basic building blocks on which every other business, even would-be competitors, depend.

These platforms are inescapable; you may opt out of one or two of them, but together, they form a gilded mesh blanketing the entire economy.