Woah, what Beijing did you go to? Did you walk in the backstreets at all? A block outside of the forbidden palace and it the streets are filled with trash and unpainted cinder block one story buildings. Even around Wangfujing I'd consider it dirty and the further outside the center you go the worse it gets.
I may a Tokyo apologist but it is by far a cleaner city than Beijing, it's just busier.
I was all around the city and a little out into the countryside for about 5 days. That time did overlap with the major mid-spring holiday in China, so maybe they went all-out with cleaning it up before tourists from other cities poured in.
I did see shoddily constructed and shabby little shacks that line some streets, yeah, but in terms of litter, I saw nothing. Although I did see one guy throw a bottle on the ground and immediately have two police grab him.
Coming home to my city in Japan and I was made incredibly aware of cigarette butts, empty coffee cans, full bottles of piss, and discarded conbini food packaging everywhere. It's definitely not California levels of wasteland here, but it's also not as clean as my time in China.
I may a Tokyo apologist but it is by far a cleaner city than Beijing, it's just busier.