Cleaniness is a second thing as the 1st rule is to survive. Population is so much it takes time and we have a very diverse and ancient culture.
You can't simply give excuse of survival for uncleanliness, I have seen people who look well-off even do the same. Also, people should self reflect a bit, and understand clean surroundings helps with mental well being, it's for one's own good.
Regarding population, it doesn't even matter, every individual only needs to take the responsibility to clean his OWN mess, the whole nation's cleanliness will take care of itself.