Consider cost of living.

What does lodging cost? if the person gains that amount, they might pay for lodging instead.

What does food cost? If the person gains that amount, they might pay for food instead.

How much can you realistically gain from recycling cans and panhandling all day? Not enough to buy food for any lasting quantity of time, you say? Yeah, they're likely going to get high to forget how badly their life sucks.