Social disapproval over time, including that expressed through government policy, has effect on culture. So, while it may not result particularly from the government doing something immediate to cause the cleanliness, I would be hesitant to assert it is independent of government action merely because it is cultural.
It is not clear to me that shame as a function of policy works in the USA.
In general, sure. It also is one of many things that influences it. Culture doesn't just arrive ex nihilo with no influence from concrete experience.
A counterpoint is Singapore and birthrates. For decades, decades, the government has tried incentivizing the native population to produce more children, and no matter what they do, they still aren't having results. Sometimes the government can only do so much and the rest is up to the people themselves.
Birth incentives don't work quite as well, because a $500 voucher doesn't go very far in a country where a public housing flat can sell for $1,000,000 and the schooling system is a pressure cooker mandating extensive paid tuition.
A more worthwhile thing to discuss is the prevalence of people ducking their heads or rushing across streets when cars approach, with a level of embarrassment that would better accompany being caught defecating in the street (well, maybe not in SF.) Our culture has so utterly failed around mobility that people are ashamed to be caught walking.
The two places where you encounter unwanted crossings in volume in the US are 1. Streets (for commerce, not travel) that were built too wide, either to accommodate too much vehicle traffic or to accommodate a despotic authority that forces wide streets(probably your local fire department or your state DOT); or 2. Stroads that do nothing well, at great expense. If it has a 45mph speed limit and stop lights, it's probably this.
What's absurd is that roads where people live and shop and walk are allowed to be unsafe for people walking.
It works, but it works against you, as Mitt Romney discovered with his "makers and takers" gaffe and Hilary Clinton discovered with her "deplorables" gaffe.
The rest of the paragraph doesn't support your main point. How do your Japanese friends scolding you on the cultural nuances of japan prove or help support your point of government policy reflecting culture?
There a huge number of examples about the influence of commercial advertising on the effect of the behavior of the Japanese consumer. Just spend sometime asking why the Japanese order KFC for Christmas or why beer is poured with a head targeted at 70/30.
I think that in some cases an outsider looking in that learns the culture might see things that the people on the inside miss as they where not born into the group think of the culture. I know my Japanese friends have at times asked my questions about the American cultural where I did a bit of a double take, forcing me to see things I just sort of went with in the past.
For anyone that has interest in seeing how Japan got where it is this book is really good...but 800+ pages and you better like history and details.