Of course, whoever left that stuff there is probably homeless and has no other place to put it. I've noticed caches of homeless stuff like this other places, too. Bus stops and park benches seem to be good places for people to deposit belongings for long periods. In recent weeks, the park at 20th and Pennsylvania has had one bench permanently occupied by a bunch of stuff underneath a tarp. The tarp is weighted down with rocks or something, and for at least a while there was a cardboard sign next to it saying something like “private, do not touch.” I guess such warnings are sort of respected b/c most people think there's probably nothing there worth taking. Perhaps most people also feel sorry for anyone who is in a position to have to leave their belongings on the sidewalk and don't want to kick those people when they're down by taking or molesting what may be their last possessions.
I also wonder if there's something about the trust, audacity, and plain strangeness of an act like this that makes people hesitate to mess with this stuff. I say that b/c when I was cycling through Europe I would regularly leave my bike in random places (like parks) while I wandered around a city or town. I would always lock it with a u-lock, but the lock was too small to lock it to anything, so generally I would just lock the wheel to the frame so the bike wouldn't roll. That obviously made the bike harder to move, but what about all my luggage that was strapped to it? I never secured that in any way. If someone had wanted to take it they would have needed only about 30 seconds to strip most of my stuff off my bike and be gone. Yet, that never happened. Why? Why did people leave my bike and my stuff alone? Like I said, maybe they just thought it wasn't worth their trouble, but I always wondered if maybe those people who might have otherwise been prone to take something that wasn't theirs just thought, “no, that person needs that stuff.”
Of course, there's one more possibility: People are generally good and don't want to steal from others or destroy their things. I think that has something to do with it, too.