It's a cost center that people don't want to fund.

And in some places like NYC you'd have to rival the police budget to make a dent in it.

Would you though? As somebody else pointed out it could be a good public works/job creation program. You could probably put 4-5 people to work cleaning up a year for less than 1 cop. I’m kind of making up numbers here but I feel like that can’t be too far off what with salary, pension, equipment, etc.

A few hundred people dedicated to taking care of litter would likely make a difference anywhere. You can get that for far less than $6 billion. You could pay 1000 people $1000/day to do it and you’d be at $365mill.