They believe someone else - a park maintenance or highway worker will pick up after them. Litter has already accumulated. Dumpsters used by businesses. Construction and demolition sites. Trucks with uncovered loads.
Litter is blown about by wind and traffic or carried by water.
It moves until trapped by a curb, building or fence. Once litter has accumulated, it invites people to add more. Highway departments spend millions of tax dollars and many hours annually picking up litter - money and time that could be used on other services. Local, state, and federal governments also spend money removing litter left by careless people. Clean communities also have a better chance of attracting new businesses than those where litter is common.