More than a few games have also fallen victim to runaway ego and perfectionism, where the designers get distracted by their own artistic visions or desire to create something revolutionary and genre-shattering and won't be satisfied until it's 'perfect', cost, publishers, and release dates be damned! (With predictable results). Combine this with people leaving the project out of frustration with the lack of forward progress and it gets harder to finish with every delay. Often, when a big goal is for the product to be up with the current technology, it becomes a self-reinforcing feedback loop of sorts when work has to be scrapped to keep up with the times. The developers simply promised more than their programmers could possibly deliver in too short a time frame.
Most of the time there is legitimate product being produced, but internal problems simply result in it falling behind schedule and being passed in the marketplace by competitors. That said, the vast majority of vaporware isn't malicious. In the most extreme cases, the developing company itself may be a total fraud. Sometimes this is intentional, done by various promoters and stockholders solely to drive up the company's share prices, lure in new investors, or create a buzz in the marketplace that will keep their name on top.
