The network effect is widely known. It is a term used to describe a situation in which the more people adopt something, the more everyone on the network benefits from it.
But there is another effect that is related to this - call it network magnetism. It is the situation where the larger a network becomes the harder it becomes for people outside the network to resist it.
In some sense its like the law of gravitation. The larger a body, the more it attracts other bodies towards itself. Think of the car. Once it reached critical mass, cities evolved in a way that you literally need mechanized transport just to survive. Or you could never get to work, or to a hospital, or to the grocery store, or anywhere, in a large city.
Or think of the Internet. If viruses, worms, and the like are such a danger, why not stay away from it ? Why not stay unconnected ? And yet, every day it becomes harder and harder to stay away. The network magnetism gets stronger by the day and in the end we all decide that there is really no alternative.
This is not just about a "fad", fads come and go, but network magnetism stays and gets stronger.
The reason for it is of course rather simple. We live in a world - humans have always lived in a world - where one person's life depends on thousands of others (think of the number of people who do their jobs just to make sure that piece of toast appears on your morning breakfast tray).
And as more people adopt a technology, or product, or custom - society starts to adapt itself to this technology. Pretty soon, you cannot order stuff except on the phone, you cannot book your tickets except on the Internet, you cannot reserve a hotel room except with a credit card, you cannot get a professional job without an expensive education (the education system itself is a network - a few hundred years ago, it was not required to go through 16 or 18 years of schooling just to make a decent living, the requirements have evolved as the educational system has evolved).
Is this good or bad ? I don't know. But its inevitable.