it helps that there's a regulatory agency that verifies the cleanup happened! if the 4th of july might get canceled the following year ppl might be more aggressive around cleaning up.
The Japanese clean up after everyone including the shitty few who don't clean up after themselves.
Compare that to USA, Go to the National Mall (the grass in DC) on the 4th of July. See it's covered in people. Check on the 5th of July. The entire place will be covered in trash and refuse.
If 2% of the people on the mall on the 4th don’t clean up after themselves and the 98% don’t pick up the slack, it will be disgusting, even if 98% of the people are responsible for their own trash. Americans draw a hard line on trash that is theirs and trash that isn’t. Japanese do not.
My theory is that in Japan people see it as their responsibility to clean up, regardless of who made the mess. In the west, most people are only concerned with their own mess.
It's kinda the opposite of "responsible for yourself," it's a civic sense that extends to include everyone and everything around you - including things that weren't directly caused by you-as-individal.
In the case of the cherry blossoms, they were planted for the enjoyment of the people, and thus the people who come to enjoy them are a part of that system. The cherry blossom viewing events where thousands of people come to picnic, only is a "thing" because thousands of people come - everyone there is a participant by virtue of attending. Thus they hold part of the responsibility for the outcome of the event and the aftermath.