Common reasons for littering are:

• unavailability of trash cans (in a convenient distance)
• inability to pay for trash disposal (this includes transport of heavy items or a large quantity of)
• creation of jobs associated with trash removal (often including arguments that tax payers fund those jobs and as a taxpayer it’s their right to litter)

Exaggerated are these issues by low social education fueling short sightedness (“out of view out of mind”). So people lacking the understanding that somebody has to pay for removal of that waste.