Why have Moore's observations and predictions held true over so many decades? Moore's Law isn't really a law at all -- in fact, there's no fundamental law of physics behind it. Moore's Law only holds true because of the actions of human beings. But what keeps the cycle going even as the challenge to make more powerful circuits grows?
Much of the reason is psychological and driven by the market. Companies that make integrated circuits are competing against each other and everyone knows about Moore's Law. That means every corporate executive has this in mind: if our company doesn't double the power of our circuits in 18 months, another company will beat us to it.
Because companies don't want to give an edge to competitors, they pour a lot of money into research and development (R&D). These R&D divisions work to develop new techniques to create smaller components and arrange them in such a way that maximizes their performance. It costs a lot of money to keep up the cycle of research, but this cost is balanced against the threat of competitors gaining a foothold and dominating the market.
Another factor is the simple desire to overcome a challenge. Many people have predicted the end of Moore's Law over the years. Some people thought it would come to an end during the 1980s. Others said the same thing in the mid '90s. It seemed like engineers would eventually bump up against a barrier that would be fundamentally impossible to breach. But engineers somehow manage to find a solution each time, keeping Moore's Law alive.
Consumers also drive Moore's Law. The rapid development of electronics has created a sense of expectation among consumers. Every year, faster and more advanced electronics hit the market. From the consumer's point of view, there's no reason not to expect something better next year.