I think you’re correct that it’s a culture of “someone else will do it.” Also, you can go further and pick up trash that doesn’t belong to you in an effort to keep the space clean for everyone: https://youtu.be/5N2eM7Za9Ss. In some cultures, it’s taboo to touch other people’s trash. In many more, it’s considered beneath the social class of people to clean up like that.

What amazed me about Provo and SLC was how clean and orderly the busy public spaces are, not just the nicer neighborhoods. There’s clean and orderly rich neighborhoods in every place in the world. Palo Alto pays people to go around and power wash everything. What’s rarer is places where even the busy tourist areas and lower income neighborhoods are clean. What you’ll see often in Tokyo are places that are not nice—worn out buildings, or buildings with mildew on white surfaces because it’s still a hot and humid country—but where the streets are clean and well kept.