Because of this man:

The reason why Japanese people keep waste in their pockets and then throw it indoors is worrying.
In 1995, the religious sect Aum Shirikyo planned a terrorist attack on the Tokyo subway, causing the death of 13 people and 6,000 injured.
They used sarin gas, a nerve gas of mass destruction.
The Japanese government then decided to remove the baskets as they were considered ideal places to hide chemical weapons .
The reasons why the sect planned this massacre have never been made clear . Their leader was sentenced to death.