Why is the weather in Chengdu the worst?

Well, after living in Chengdu for a while, I feel similar to what you said, that is, it is cloudy, and it may be sunny or rainy in the afternoon. I think it's because Chengdu is located in Sichuan Basin, with hot and humid climate and high water content, so there are many changes. If you are in Inner Mongolia, there are four kinds of weather in a year, sunny or snowy or rainy or cloudy.