It takes so long in LA and other American cities because so many proposals have to be vetted before so many people before anything gets approved. Most of the time, the NIMBYism takes over and no progress is made. By contrast, according to the article, this is what happens in Chinese cities:
At the risk of only slight oversimplification, the system works like this: Planners draw subway lines on a map. Party officials approve them. Construction begins. If anything is in the way, it is moved. If they need to, Chinese planners "just move 10,000 people out of the way," said Lee Schipper, a transport planner who has worked with several Chinese cities in his role as director of research for EMBARQ, a Washington-based transportation think tank. "They don't have hearings."