Slot machines are prevalent in Las Vegas because they are a popular form of entertainment that capitalizes on human psychology. They are designed to create a 'scarcity loop' with opportunity, unpredictable rewards, and quick repeatability, which can be very enticing and addictive. People are drawn to the chance of winning money, despite the common knowledge that 'the house always wins.' This loop is not only found in slot machines but is also used in various industries, including social media, sports gambling, dating apps, and the gig economy, to encourage repetitive behavior.