I know this is late, but I wanted to give you a response.

99% of the year every Tokyoite is clean and respectful of the city and the personal space of others. They don't get much approved days where they can let loose on the streets. Maybe some summer festivals and impromptu gatherings at Yoyogi park but that's it. What I've noticed after all these events, Halloween in Shibuya included, there are participants and neighborhood people that go out and help clean the mess. I helped clean after one, i think it was 2017. I asked someone else why they were doing it and their response was basically "I do it so everyone else can continue having fun." They weren't complaining about picking up other people's garbage and they didnt want the event to be cancelled in the future either.

The pressure at the bottom is great in their society and cancelling halloween in Shibuya was the wrong decision, they should have just expanded it to other areas to help control crowds and block off more streets for pedestrians that night only. I'm sorry you didnt enjoy it, I dont like parties usually but I always had a blast at them. I think my first one was 2009 and if I was in China for work I would always take a vacation to visit my friends at that time.