Options :-
Too poor to afford a coat

Less clothing to take off at night (when out clubbing / copping off)
Infection from dodgy tattoo's provide enough tingling warmth in the skin that additional clothes are unnecessary
They are surrounded by warm air bubble every time they open their mouths
Less items to get strangled with / pulled off in their daily scrap
More excuse to bag a bag of chips on the way home - to keep warm like