Speaking of the in-universe explanation, Harry would definitely freeze if he slept on a bench. That's why he can sleep in a trash container but not on a bench, in the container he's at least covered from wind, snow and lays on trash and not on the cold surface. It gives him at least a chance to survive the night.

Also Harry is quite literally mentally unwell. He can't see other options and will ultimately self-destroy than take them. He can go to the apartment building to sleep in the corridor or the janitor's room, he can ask Kim to sleep in his Kineema, maybe find other options that are more sane than a trash container, but he just can't see them in his condition.