重庆为什么直辖？这个问题的答案可以从多个方面进行解释。以下是对这个问题的解析以及英文翻译对照：

首先，重庆直辖市的设立是为了解决四川省人口过多、地势复杂、交通不便等问题。在1997年之前，重庆市是四川省的一个地级市，由于人口众多、地势复杂，导致交通不便，不利于经济发展。为了解决这个问题，国家决定将重庆市从四川省分出，设立为直辖市，从而加快其经济发展和城市现代化进程。英文翻译为: The establishment of Chongqing as a municipality is to solve the problems of overpopulation, complex terrain, and transportation inconvenience in Sichuan Province. Before 1997, Chongqing was a prefecture-level city in Sichuan Province. Due to its large population and complex terrain, transportation was inconvenient, which was not conducive to economic development. To solve this problem, the state decided to separate Chongqing from Sichuan Province and establish it as a municipality to accelerate its economic development and urban modernization process.

其次，重庆直辖市的设立也是为了推动长江上游地区的经济发展。重庆市位于长江上游地区，是长江流域的交通枢纽和经济中心。将重庆市设立为直辖市可以更好地发挥其在长江上游地区的辐射作用，带动周边地区的经济发展，从而更好地推动长江流域的经济发展。英文翻译为: The establishment of Chongqing as a municipality is also to promote the economic development of the upper reaches of the Yangtze River. Chongqing is located in the upper reaches of the Yangtze River and is a transportation hub and economic center of the Yangtze River Basin. Establishing Chongqing as a municipality can better leverage its radiation effect in the upper reaches of the Yangtze River, drive the economic development of surrounding areas, and thus better promote the economic development of the Yangtze River Basin.